Data Center Glossary of Terms

Our glossary is meant to provide definitions to terms and phrases often used in the data center industry.

ACL
Access Control List.

ACPI
Advanced Configuration and Power Interface.

ACWP
Actual Cost for Work Performed.

AD
Active Directory.

ADO
ADO: Microsoft® ActiveX® Data Objects. 

ADS
Active Directory Service or Active Directory Structure.

AGP
Advanced Graphics Port. Graphics card interface for high performance graphics.

AMR
Audio/Modem Riser. An Intel specification that aims to eliminate legacy support for audio and modem functions on motherboards. It allows analogue functions (i.e. both audio and modem) to be handled by a separate riser card.

AMS
Acquisition Management System.

ANSI
American National Standards Institute.

APC
American Power Conversion. Company that has made a name for itself supplying UPSs.

API
Application Programming Interface. The definition of procedures (and protocols) that a software application can make use of.

APP
Asynchronous Pluggable Protocols.

AppleTalk
Macintosh computers networking protocol.

Application Failover
The capability of an application to recover from the failure of a database that the application is connected to and for the application to switch over to using the surviving instance thereby providing no loss of data or continuity.
Also known as ‘run-time failover’.

Approved for Construction (AFC) Drawing
A final drawing approved by the Design
Engineer and local municipality for the purpose of construction 

ASCII
American Standard Code for Information Interchange. In ASCII the letters of the alphabet, digits and various punctuation symbols are assigned a unique 7 bit number (0-127). 
On most systems there is also an additional set of 128 "extended ASCII codes" that are used to represent a variety of other symbols. These extended codes are not part of the ASCII standard.

ASDL
1. Asynchronous Digital Subscriber Line. Provides a permanent link to the internet.
2. Asymmetric Digital Subscriber Line. Technology allowing high data rates over existing copper telephone lines.

ASHRAE
American Society of Heating, Refrigeration and Air Conditioning Engineers

ASIC
1. Application Specific Integrated Circuit. A circuit (or chip) design for a specific application, typically built up using building blocks of existing circuit designs.
2. American Society of Irrigation Consultants.

ASIO
Audio Stream Input/Output.

ATMP
Ascend Tunnel Management Protocol.

BAC
Budget At Completion. The total of all budgets allocated to a project, includes for example the budgets allocated to any sub-projects.

BDC
Backup Domain Controller.

BDN
Borland Developer Network.

BDRP
Business Disaster Recovery Plan

BCWP
Budget Cost for Work Performed.

BCWS
Budget Cost for Work Scheduled.

Beep
Blocks Extensible Exchange Protocol. A set of building blocks for creating customised protocols.

BIND
Berkley Internet Name Domain.

BIS
Business Information Systems.

BITS
Background Intelligent Transfer Service.  

Blue Screen
Terminal error screen displayed by Microsoft Windows, not normally recoverable except by a reboot. Also known as a Stop Screen. A blue screen will display a STOP error code, which may give some indication as to the cause.

BMS
Building Management Systems or Building Automation System

BOM
Bill of Materials.

BOOTP
Bootstrap Protocol. Protocol allowing (possibly) diskless network computer to be booted, downloading configuration (such as IP address) and the operating system from a server over the network.

bps
Bits Per Second. Used when specifying connection speeds across networks. When calculating the maximum throughput across a network remember that network communications itself has some overhead. As a rule of thumb therefore divide by 10 to get the number of bytes that this equates to.

For typical connection speeds this equates to:

Actual throughput rates may be less than this because of other factors such as other network traffic.

BTU
British Thermal Unit. BTUs are typically used to rate air conditioners (and some heaters). One BTU is defined as the energy required to increase the temperature of one pound of water by one degree Fahrenheit. To convert from BTUs to KWs: use 1 watt = 3.4129BTUs. This means that for typical air-conditioners:

For air conditioners the typical power consumption will be less than half their cooling rating.
As a guide: 1 person approximates to 500 BTU and one PC approximates to 500 BTU.

Budget
A fiscal plan, usually for a given time period and/or for a given project  

CAL
Client Access License.

CCSE
1. Check Point Certified Security Expert.
2. Center for Computational Sciences and Engineering, at Berkeley.

CDMA
Code Division Multiple Access, a third generation digital wireless technology.  

CGI
Common Gateway Interface. Interface standard allowing programs to interface to web servers. CGI programs can be written in any compilable language. CGI programs are executed on the server, normally in response to some input from a web page.

Checkpoint
At a database checkpoint the database flushes out data not yet written to disk.

CI
1. Continuous Improvement.
2. Customer Intelligence.

CIPI
Critical Infrastructure Protection Initiative.
Clamping level.
The voltage level above which a surge suppression device diverts energy away.

Clamping time
The response time for a surge suppression device, i.e. the time it takes to respond to the voltage climbing above the clamping level.

CLI
Call Level Interface.

CLR
Common Language Runtime. The CLR executes .NET code and is similar in concept to the Java Virtual Machine.  

COA
Certificate Of Authentication.

COM
1. Component Object Model. Defined by Microsoft.
2. Computer Output on Microfilm.

Configuration Management
Configuration Management is a discipline to ensure that the configuration of an item (and its components) is known and documented and that changes are controlled and tracked.

Connection Failover
Where if the server that an application wants to connect to is unavailable then a connection is made instead to a second server.

Connectionless (protocol)
A protocol where there is no handshaking between the sender and receiver. In a connectionless protocol neither the delivery of messages nor the correct sequencing of messages is guaranteed

Connection Oriented (protocol)
A protocol where a connection must be established before hosts can exchange data.

CPA
Cost Per Acquisition.

CPC
1. Cost Per Click (or Pay Per Click). Term used by affiliate programs indicating a payment rate per advertisement click.
2. Computer Power Center. Term used to describe power distribution unit that combines two PDU's and a static switch

CPM
Cost Per iMpression (or Pay per iMpression). Term used by affiliate programs indicating a payment rate based on number of impressions (or displays) of an advertisement.

CPP
Customer Preview Program. System for allowing customers to preview a product before its general release.

CPR
Cost Performance Report. A report showing cost and schedule information.

CPS
Cost Per Sale (or Pay Per Sale). Term used by affiliate programs indicating a payment rate for a for a sale.

CRAC
Computer room air conditioner

Critical Awareness
Being fully mindful and observant of the building’s Critical Systems and Environments

CRM
Customer Relationship Management. 

CSV
Comma Separated Value. Typically a text file containing values with comma delimiters (i.e. commas separating distinct fields).

CTR
Click Through Rate. Abbreviation used by affiliate networks. Is the percentage of the number of advertisement displays that resulted in a click.

CTS
Clear To Send. Used as part of serial hardware flow control.  

DAC
Discretionary Access Control. Provides detailed access control on files and resources.

DAT
Digital Audio Tape. Originally developed for audio recording.

Data Center
The department that houses the computer systems and related equipment, including the data library. Data Entry and systems programming may also come under its jurisdiction. A control center is usually provided that accepts work from and releases output to user department.

Database Connectivity
Connecting and communicating between an application and a database system.

Data mining
Generic term for identifying possible relationships and trends between data items. Typically data mining is the statistical analysis of data to identify commonalities and patterns.

DDK
Device Driver Kit. Normally used to refer to the Microsoft Windows Driver Development Kit.

Denial of Service\
Denial of Service is an attack on a system (typically a server or a network) that aims to crash, block or overload the system and thereby deny its services to others. A denial of service attack is illegal in most countries.

DFM
Design For Manufacturing.

DFS
Distributed File System. Simplifies the process of creating a single directory hierarchy that includes multiple file servers and shared folders in a group, division or enterprise.

DHCP
Dynamic Host Configuration Protocol. Communications protocol where a range of IP addresses are managed centrally and assigned automatically to computers on demand. The alternative is to use static IP address where each computer is permanently allocated a fixed IP address.

Disk Thrashing
On a system with Virtual Memory, pages of memory are read from and written to the swap file as necessary. Disk Thrashing is when there is excessive paging, specifically when the I/O system is busy paging memory but the CPU is not fully utilized - generally if the system is unresponsive (i.e. slow) and there is lots of disk activity then the system is likely to be thrashing.

If disk thrashing is a problem then a short term solution may be to reduce the number of running applications. A longer term solution is to add more memory.

DLT
Digital Linear Tape. Tape storage developed in the late seventies by Digital Equipment Company, and the basis for successive generations of DLT tape drive which higher storage capacities and transfer rates. Most DLT drives are backwards compatible but check. DLT tapes use half inch tape media, fully enclosed in a sealed case which is designed only to open when the tape is in the drive.

DPC
Data Processing Center

EAC
1. Estimate at Completion. The estimated cost of a project when it is completed. This includes all project costs to date plus an estimate of any remaining project costs.
2. EAC—Environmental Air Conditioner (also known as computer room air conditioning unit or
CRAC)

ebXML
The convention which enables businesses to carry out business transactions via the Internet, irrespective of their location and size. This provides companies with a standardised method of exchanging messages and supporting trading relationships, data communications an defining and registering business processes.

EDRP
Encrypted Data Recovery Policy. Controls who can recover encrypted data if the owner's private key is lost.

EFS
Encrypting File System. Strengthens security by encrypting files on the hard disk so that no one can access them without using the correct password.  

Environmental Loop
Critical secondary chilled water piping which supports cooling
requirements in the Critical Environment

EOL
End Of Life. Typically used where a product has reached or is near reaching the end of its supported life and customers are being encouraged to upgrade to a newer version.  

EPO
Emergency Power Off

ETC
Estimate to Completion. Estimate of work and/or costs (remaining) to complete a project.

EULA
End User License Agreement.

EUP
Enterprise Unified Process .

FAT
File Access Table. More commonly referred to as FAT16 following the advent of FAT32. Uses 16-bit addressing. DOS and Windows 3.x machines commonly use FAT16.

Fat Client
A client/server application that performs most of the processing itself rather than at a server

FCB
File Control Block. FCB introduced in the first version of MS-DOS. Because FCBs predate a hierarchical directory structure they can only be used with files in the current directory. Superseded for most purposes by file handles.

FDD
1. Floppy Disk Drive.
2. Feature Driven Process.

FDDI
Fibre Distributed Data Interface. One type of LAN technology.

FIPS
Federal Information Processing Standard. A set of standards and guidelines developed by the US National Institute of Standards and Technology (NIST) for US government agency use.

Firewall
A program (or set of programs) which prevents unauthorised access to a network or to an individual computer.

FQON
Fully Qualified Object Name. The four parts of an object's name - its server, its instance, its owner and its name.

FTP
File Transfer Protocol. Used for transferring files across networks.

Full Duplex
Data can be sent and received simultaneously and at the same speed

Gantt chart
A type of bar chart used for project management. Each task is illustrated as a horizontal bar on a chart, with time along the horizontal axis and tasks along the vertical axis.

GB
Giga-byte. In computing generally taken as 1,073,741,824 bytes (i.e. 1024 x 1024 x 1024), except that storage devices are sold by manufacturers with 1GB = 1,000,000,000 bytes.

Geocoding
A way of importing non-map data into a Geographical Information System such that its geographic properties can be identified and its coordinate position identified. Coordinate points are assigned to the data so that it can be used on its own to display the location of (each) object.

Georeferencing
Using an overriding coordinate system so that different sources of geographic data can be referenced to the Earth's surface in the same way. .

GIS
Geographic Information System(s). Tools for managing, analysing and modelling geographic data.

GMT
Greenwich Meridian Time.

Gopher
An internet protocol designed for distributed document search and retrieval - Gopher allows databases to be searched.

GPMC
Group Policy Management Console.

GPO
Group Policy Object (under Windows 2000).

GPRS
General Packet Radio Service. Intended for data transmission, typically for wireless internet.
Descriptive article on GPRS.

GPU
Graphics Processing Unit.

GSM
Global System for Mobile communications. An established and globally accepted standard for digital wireless communications.

GUI
Graphical User Interface.
GUID
Globally Unique Identifier

Half Duplex
Allows simultaneous sending and receiving of data, but data is sent at a lower speed than it is received.

HDD
Hard Disk Drive.  

HMI
Human Machine Interface.  

Hot (Standby) server
A backup server that is powered up and ready to take over from a primary server should the primary fail. The standby server may automatically take over or may require minimal intervention to do so depending on the configuration.

HTML
Hyper Text Mark-up Language.

HTTP
Hypertext Transfer Protocol. Network protocol for the transfer of web or intranet pages (for subsequent display or other purpose).

HTTP-R
Reliable Hypertext Transfer Protocol. A protocol that enables messages to be reliably transported between two applications via the Internet.

HTTPS
Secure Hypertext Transfer Protocol.

Hub
Generic term for any device which connects two or more computers or devices together on a network allowing them to communicate.

IANA
Internet Assigned Numbers Authority.

IBG
Institute of British Geographers.

Icann
Internet Corporation for Assigned Names and Numbers.

ICAO
International Civil Aviation Organization.

ICF
Internet Connection Firewall. Abbreviation used by Microsoft to refer to the firewall built into Windows XP.

ICS
Internet Connection Sharing. Abbreviation used by Microsoft to refer to the internet connection sharing facility built into more recent versions of Windows. Allows multiple computers to share a single internet connection which is provided by one computer in a group.

IDE
Integrated Development Environment.

IE
Microsoft Internet Explorer

IETF
Internet Engineering Task Force.

IES
Illuminating Engineering Society

IIS
Microsoft Internet Information Services.

IMAP
Internet Message Access Protocol. A protocol for accessing electronic e-mail (or bulletin boards). IMAP allows e-mails to be read by a client but still be stored on a central server. IMAP is suited to environments where people need to be able to access their e-mail from more than onw workstation.

IMD
Index of Multiple Deprivation. Provides a guide to the extent various types of deprivation within a geographic area.

IMHO
Abbreviation: In My Humble Opinion.

InProcHandler32
The optional registry key ‘HKEY_CLASSES_ROOT\CLSID\{16-byte ID}\InProcHandler32’ identifies the library that handles the RPC communications for the COM object.
Associated keywords: COM, Registry, InProcServer32

InProcServer32
The registry key ‘HKEY_CLASSES_ROOT\CLSID\{16-byte ID}\InProcServer32’ holds the full path to a DLL if the COM object is implemented as a library. If this key does not exist then it is assumed that the COM object is managed by a separate process, with LocalServer32 holding the full path name of the executable. Associated keywords: COM, Registry, InProcHandler32, LocalServer32.

Intranet
Private network using internet type tools, but available only within an organisation.

Internet
Worldwide system of linked networks, providing data communications services including file transfer, electronic mail, World Wide Web and newsgroups.

Inverter
The part of a ups that converts the battery DC output to AC.

IOL
Internet Operating Environment.

IP
Internet Protocol. IP specifies the format of packets (called datagrams) containing data and a destination address. IP is often combined with tcp

IPS Tag
Nominet is the registry for UK domain names and almost all hosting companies will have an IPS tag (also known as a Nominet Provider tag) which signifies membership of Nominet. It is a single alpha-numeric sequence, in uppercase, sometimes hyphenated.

IPSec
Internet Protocol Security (also abbreviated to ip Security). Encrypts tcp/ip traffic to secure communications within an intranet and provide the highest levels of security for vpn traffic across the Internet.

IPX
Novell Network networking protocol.

IRC
Internet Relay Chat.

IRQ
Interrupt request number.

IS
Information System(s).

ISAPI
Internet Server API. A standard set of functions for interfacing to Microsoft's Internet Information Server

ISAM
Indexed Sequential Access Method.

ISDN
Integrated Services Digital Network. Digital modem line. Provides higher speeds than K56/V90. Single channel ISDN provides speeds of 56K to 64K. Dual channel ISDN provides speeds of 110K to 128K.

ISO
International Organization for Standardization.

ISP
Internet Service Provider.

IT
Information Technology.

ITC
1. Information and Communications Technologies.
2. Integrated Circuit Technology.
3. Institute of Computer Technology.

ITE
Integrated Translation Environment. (Borland development/translation tool.)

J2EE
Java 2 Enterprise Edition. A development environment which is independent of hardware systems and operating systems. The idea is that software developers need only write applications once and these applications can then be run unchanged on any computer or operating system.

J2SE\
Java 2 Standard Edition.

Java
Object oriented programming language developed by Sun Microsystems, designed for platform independence and frequently described as "write once run anywhere" language.  Sun describe Java as "A simple, object-oriented, distributed, interpreted, robust, secure, architecture neutral, portable, high-performance, multithreaded and dynamic language."

JDBC
Java DataBase Connectivity. Database access interface based on ODBC for use within Java.

JFC
Java Foundation Classes.

JNDI
Java naming and Directory Interface.

JNI
Java Native Interface. Allows Java developers to utilize platform specific code that runs outside of the Java Virtual Machine. 

JRE
Java Runtime Environment.

JSP
1. JavaServer Pages. JSP allows web pages to be generated dynamically using a combination of XML tags and Java Servlets. JSP is an extension to Java  servlets allowing the dynamic generation of web pages. cf ASP  2. Jackson Structured Programming.

JSTL
Java Standard Tag Library.

K56/V90
Modem standard for transmitting data across a telephone line. Provides a maximum of 56kbps download and 33kbps upload.

KB
Kilo-byte, 1024 bytes.

kbps
Kilo-bits per second. Strictly 1024 bits per second (bps), i.e. 1kbps = 128 bytes per second. Normally taken to mean 1000 bps, i.e. 1kbps=125 bytes per second. When estimating network/modem throughput, a figure of 1kbps=100 bytes per second is probably closer to the real throughput after other networking overheads are taken into consideration.

KISS
Keep It Simple Stupid.

KVA
Thousand VA

LAN
Local Area Network. Usually a high speed network, normally confined to a single geographic area, allowing communications at either 10Mbps, 100Mbps or (rarely but up-coming) 1000Mbps.

LANs are typically implemented using Ethernet, Token Ring, Fast Ethernet, Fibre Distributed Interface (FDDI) Asynchronous Transfer Mode (ATM)or LocalTalk.

LBS
Location Based Services.

LCD
Liquid Crystal Display.

LDAP
Lightweight Directory Access Protocol.

LED
Light Emitting Diode. Small light found on many items of equipment, typically used to indicate activity or that something is switched on.

LGWR
Oracle: LoG WriteR process. LGWR writes redo information from the log buffer to the redo log files. LGWR is also responsible for performing checkpoints.

lmhosts
A text file that is used to manually configure Netbios names. In NT it is located in the directory C:\WinNT\System32\Drivers\Etc.

LocalServer32
The registry key ‘HKEY_CLASSES_ROOT\CLSID\{16-byte ID}\LocalServer32’ holds the full path to the COM executable.

lol
1. Laughing Out Loud.
2. List of Links.
3. List of Lists.

LRU
Least Recently Used. Many caching algorithms using a LRU algorithm, removing from the cache the least recently used item.

LVD
Low Voltage Differential (device). LVD supports SCSI data transfer rates of up to 80MB/sec, up to 16 devices and cable lengths of up to 25 meters with one device or 12 meters with 16 devices attached.
MAC
1. Media Access Control.
2. Apple Macintosh computer 

MAC address
Media Access Control address. Unique hardware serial number that uniquely identifies a device on a local area  network (commonly a NIC) (Sometimes also referred to as a NIC's "physical address".)

A MAC address is 6 bytes in length (i.e. 48 bits) and is normally written as a 12 digit hexadecimal number, with dashes or colons between each pair of hexadecimal digits. The first three bytes identifies the manufacturer and the second three bytes represent a unique serial number generated by that manufacturer. MAC addresses should therefore always be unique (although some cards and switches allow the MAC address to be cloned).

Main Gas Line
The primary gas distribution piping serving a building

Main Incoming Electrical Feeder
The primary electrical service to a building from the utility
company

MAPI
Messaging Application Programming Interface. A common interface standard (originally specified by Microsoft) enabling applications to interface to messaging systems.

MB
Mega-byte. In computing this is generally taken as 1,048,576 bytes (1024 x 1024). Storage devices usually define this as 1,000,000 bytes.

mbps
Mega-bits per second. Strictly 1mbps = 128KB per second, but when measuring network/modem throughput a figure of 1mbps = 100 KB per second is probably closer to the real throughput after other networking overheads are taken into consideration.

MBR
Master Boot Record.

MCSE
Microsoft certified systems engineer.

MDI
1. Multiple Document Interface. A GUI interface for a tool allowing more than one document to be visible at a time.
2. Medium Dependent Interface. Provides the physical connection to a cable.

MDI/MDI-X
Network hub crossover switch. An MDI/MDI-X switch on a network hub typically allows a port on a network hub to connect to either a network peripheral (such as a pc) or another hub/switch.

MDIX (or MDI-X)
A cross over version of MDI. MDI ports connect to MDIX ports via a straight through cable, both MDI-to-MDI and MDIX-to-MDIX connections use crossover cables.

MEP Systems
Mechanical, Electrical and Plumbing Systems

MFC
Microsoft Foundation Class Library. Provides a framework on which applications can be developed for MS-Windows.

MHP
Multimedia Home Platform.

MIDAS
Middle-tier Distributed Application Services. Borland physical multitier architecture used in Delphi. Renamed as DataSnap in Delphi 6.

MMC
Microsoft Management Console.  

MII
1. Media Independent Interface.
2. Microsoft/Intel/IBM.

MMC
Microsoft Management Console. The Microsoft Management Console provides an open, extensive, common console framework for management applications. The intent is for it to provide a common style of user interface for administering networks, computers, services and other system components.

MME
Microsoft Mobile Explorer. Mobile phone/WAP emulator, allowing you to see what a web site would look like on a WAP capable phone.

MMI
Man Machine Interface. Same as HMI  but an older term and generally regarded as being less politically correct than HMI.

Modem
Short for Modulator/Demodulator. A modem allows allows data to be transmitted over an analog stream (typically a phone line) to another modem where the data is reconstituted.

MOLAP
Multidimensional-OLAP

MRP
Machine Readable Passport.

MRTD
Machine Readable Travel Document.

MRV
Machine Readable Visa.

MRZ
Machine readable zone. On  ICAO  9393 compliant passports this is where the machine readable data is located.

MSDE
Microsoft Data Engine. Database engine that can be distributed royalty free with applications built using Visual Studio or Office 2000 (some conditions may apply).

MSDE 1.0
Microsoft Data Engine compatible with SQL Server 7. See also MSDE.
Microsoft Data Engine compatible with SQL Server 2000.

MSDN
Microsoft Developer Network. 

MSP
Media Service Provider.

MTBR
Mean Time Between Failures.

MTS
1. Multi-Threaded Server (Oracle). Oracle definition: MTS allows many user processes to share very few server processes. Without MTS each user process requires its own dedicated server process; a new server process is created for each client requesting a connection. A dedicated server process remains associated to the user process for the remainder of the connection. With MTS many user processes connect to a dispatcher process. The dispatcher routes client requests to the next available shared server process. The advantage of MTS is that system overhead is reduced, so the number of users that can be supported is increased. 
2. Microsoft Transaction Server.

MTTR
Mean Time To Repair.

MTU
Maximum Transmission Unit. The maximum amount of data that can be sent across an interface without being broken up into more than one message or packet.

NameServer
Alternative name for a  DNS server.

NAS
Network Attached Storage. Typically a data server on a network that provides file storage accessed via the network.

NAT
1. Network Address Translation - translates multiple IP addresses on a private LAN  to one public address used on the Internet.
2. Network Address Translator - when applied to a device that sits between two network domains and maps addresses from one network domain to another.

NAT/Firewall
A  NAT device that acts as a firewall, filtering network packets entering or leaving a network.

NBNS
NetBIOS Name Server.

NCSA
National Center for Supercomputing Applications.

NetBEUI
Network protocol for Windows NT networks.

NetBIOS
Network protocol for LAN Manager and Windows NT networks.

Network Connectivity
Connecting and communicating between two or more computers, typically over a network.

Network Protocol
Standards that allow computers to communicate. Protocols also define ways of handling lost or damaged data packets. The main types of network protocol are:

• HTTP
• FTP
• TCP/IP
• IPX
• DECnet
• AppleTalk
• NetBIOS/NetBEUI

• Star. All computers are connected to a central hub.
• Ring. Each computer is connected to two others, such that starting at any one computer you can trace the connection through each computer back on the ring back to the first.
• Bus. All computers are connected to a central cable, normally termed bus or backbone.
• Tree. Group of start networks each connected to a linear backbone

NER
Network Equipment Room

NFPA
National Fire Protection Association

NIC
Network Interface Card. Provides the physical connection between the computer and network.

NMI
Non-Maskable Interrupt.

NPD
New Product Development.

NSAPI
Netscape Server API.  API for interfacing to Netscape servers.

NT4
Microsoft Windows NT 4 (workstation or server).

NT4SP6
Microsoft Windows NT 4 (workstation or server) with service pack 6.

NTFS
File system developed by Microsoft for Windows NT. Supports long file names, journaling, security access restrictions lazy-write (allowing disk writes to be cached).

NTP
Network Time Protocol. A protocol for ensuring accurate sychronization of time (i.e the clock) between computers across a network (such as the internet).

OBDR
One Button Disaster Recovery. Disaster recovery feature provided by some tape drives. This allows the tape drive to be switched into disaster recovery mode - where its firmware emulates a bootable CD-ROM allowing the system to boot from the tape device and restore the system from the last backup.

OBS
Organizational Breakdown Structure. Structure chart normally shown as a tree diagram showing the management structure of an organisation.

OCR
Optical character recognition.

ODBC
Open Database Connectivity. Open standard developed by Microsoft aiming to provide a consistent interface to relational databases regardless of which database engine is used (e.g. SQL Server, Oracle or MySQL). In theory to migrate to another database should only require the installation of the appropriate ODBC driver for the new database.

Whilst ODBC does successfully address many of the issues involved in migrating from one database to another, there are issues outside the scope of ODBC which can (for some applications) have serious implications when migrating databases.

ODP
Open Directory Project. 

OEM
Original Equipment Manufacturer.

OGC
Open GIS Consortium. Organisation dedicated to the creation of standards in the field of Interoperable geospacial systems.

OLAP
On-Line Analytical Processing.

OLCP
On-Line Complex Processing.

OLE
Object Linking and Embedding. OLE was later enhanced and renamed by Microsoft to COM and OLE controls to ActiveX controls.

OLTP
On-Line Transaction Processing. Any number of (typically many) concurrent users adding and modifying data. Typically includes order processing, banking, stocks, and e-commerce applications.

OO
Object Orientation.

OOA
Object Oriented Analysis.

ODO
Object Oriented Design.

OOSD
Object Oriented Structured Design.

OPEN
Object Oriented Process, Environment and Notation.

Open Source
Program code that is made available for view, reuse and modification by others, normally with no license fee or restrictions on use

Operating System Authentication
1. The process of an operating system authenticating a user prior to logon or prior to connection. 
2. The process of an application (such as a database) requesting confirmation from the operating system to confirm that a user has been authenticated. This may also include the retrieval of additional user information from the operating system (such as access rights).

Operational Risk
The risk of loss (financial or otherwise) due to failings of information systems, business processes or internal controls. Operational risk therefore includes computer failures, faulty software, incorrect data entry, natural disasters, regulatory changes etc.

OPCS
Office for Population Censuses and Surveys.

OPM
1. US Office of Personnel Management.
2. Object Process Methodology. A symbolic representation of the objects and processes within a system, integrating both object-orientation and process-orientation into a single representation.

opt-in e-mail
Web marketing term for e-mail that recipients have previously requested or agreed to receiving. Typically this consent is given when registering details on a website by ticking (or leaving ticked) a box saying that you wish the company to keep you informed of products/services or that the company may share your information with other companies and organisations. 

ORDBMS
Object Relational DBMS.

OSD
Open Source Definition.

OSI
1. Open Systems Interconnection. See  OSI 7 Reference Model.
2. Open Source Initiative. A non-profit organisation dedicated to managing and promoting the OPEN SOURCE Definition for the good of the community.

OSI 7 Layer Reference Model
A reference model for communication protocols designed to allow open systems interconnection.

The seven layers are:
1. Physical
2. Data link
3. Network
4. Transport
5. Session
6. Presentation
7. Application

OSS
 OPEN SOURCE Software.

OT
Short for "Off Theme". Shorthand used in newsgroups to indicate that a posting is drifting off the topic for the newsgroup.

OTC
Order To Cash.

OTN
Oracle Technology Network.

OTOH
Shorthand for "On the other hand".

PAD file
Portable Application Description file. A file containing product descriptions, specifications and other information, expressed in format consistent with the PAD specification. This allows software publishers to disseminate information about a product in a consistent format.

Palladium
Code name for an initiative from Microsoft aiming for features greater data security, personal privacy and system integrity. Will build upon TCPA.  For a discussion on Palladium/TCPA

Panel Schedules
A list of loads connected to an electrical panel.

Pay Per Click
Pay Per Click, often abbreviated PPC. Where a company (or advertiser) pays (a search engine or affiliate site) for each click-through.

PBX
Private Branch Exchange.

PCB
Printed Circuit Board.

PCM
Oracle: Parallel Cache Management

PCML
PCML: Patter and Component Markup Language

PDC
Primary Domain Controller.

PDM
Product Data Management.

PDU
Power Distribution Unit.

PDW
Package and Deployment Wizard.

PE
Portable Executable. Typically Java (running on a Java Virtual Machine) or .NET (running on CLR).

Pert
Program Evaluation Review Technique.

Pert chart
A PERT chart is a type of chart used for project management. It represents each task of a project as a box (circle or rectangle), arrows between tasks are used to show the sequence and task dependencies (i.e. which tasks need to be complete before others can start). Also known as a Network Chart, a precedence diagram and logic diagram.

PFI
Pay For Inclusion. Normally refers to a search engine that will only include a site in its database in return for a fee.

PGA
Oracle: Program Global Area. The PGA is a memory region containing data and control information for a single process (server or background). One PGA is allocated for each server process, the PGA is exclusive to that server process and is read and written only by Oracle code acting on behalf of that process. A PGA is allocated by Oracle when a user connects to an Oracle database and a session is created.

Photogrammetry
The science of measuring objects from photographs.

PHP
A general purpose (server side) scripting language for web development that can be embedded in HTML.

Ping
1. Widely available network utility, Ping performs a simple network connectivity test between the current network location and a remote one. Originally named after the "ping" from sonar, the idea was later introduced that it stood for "'Packet INternet Groper'".
2. Some network games display a "ping count", "ping value", "ping" or "pinging" value. This is an indication of how long it takes to send a packet of information to a remote computer and get a reply. The values are typically in milliseconds. For gameplay generally the lower the ping count the better.

Pinging
1. Using ping to check basic network connectivity.
2. In an Oracle Parallel Server database pinging refers to the situation where two (or more) servers are repeatedly needing to access the same blocks of data. The blocks are thus said to "ping" between them (because really only one server can access the block at a time).

PKI
Public Key Infrastructure. PKI ensures that, for an online transaction, the person is who they say they are and that no-one else has access to the information. Under PKI a digital certificate is generated by a trusted third party Certificate Authority (CA)  and verified by a Registration Authority (RA).This digital certificate is a unique electronic signature and is used to generate personalised encryption keys. The certificate can also be co-signed by a financial institution, such as a credit company to provide financial credentials of the holder. The CA also issues a means to encode a message and to translate the reply using both public and private key arrangement based on the users digital certificate.

Plug and Play
Technology where adapters can be automatically configured by the system without user intervention.

PnP
Plug and Play.

PL/SQL
Oracle's ( RDBMS) Procedural Language extension to SQL.

Polygon
A continuous area defined by sets of bounding closed lines.

POP
Post Office Protocol. A protocol for accessing e-mail, allowing e-mails to be downloaded form a server, stored locally and therefore available for off-line reading.

POP 3
See POP. The version of POP adopted is version 3, hence the name POP3.

P+P
Postage and Packing.  

PPM
1. Pence Per Minute - a charge rate per minute.
2. Pence Per Message - a charge rate per message.

PPP
Point-to-Point Protocol.

PPTP
Point To Point Tunneling Protocol. Point-to-Point Tunneling Protocol is a network protocol that provides secure transfer of data from a remote client to a server. PPTP supports multiple network protocols (IP, IPX, and NetBEUI) and can be used for secure, on-demand, virtual private networking over public and private networks.

PPV
Pay Per View.

POTS
Plain Old Telephone Service.

PRS
Premium Rate Service. A service provided at a higher cost but normally with better features or performance than a non-premium rate service.

PSP
Professional Support Partnership.

PSTN
Public Switched Telephone Network.
 
PWB
Printed Wiring Board. Same as PCB, but in Japan is normally referred to as PWB to avoid confusion with "Polychlorinated Biphenyls (PCBs)" which is a poison.

QOS
1. Quality Operating System.
2. Quality of Service. Networking term for guaranteed throughput based upon measurable transmission rates, error rates and other factors. \

RA
Registration Authority.

RADIUS
Remote Authentication Dial-In user Service (W2K). Support for dial-up networking. Provides authorization, identification, authentication and accounting services for distributed dial-up networking.

RAID
Redundant Array of Inexpensive Disks. The basic idea is to combine a number of disk drives to give better cost, performance, capacity and reliability than could be achieved by a single disk.

RAID level
RAID level is a number implying the organisation of the disks in the RAID array:

RCCP
Rough Cut Capacity Plan.

RCS
Revision Control System. A version control system from GNU.

RDO
Remote Data Objects.

Redundancy
A backup system or component

RPC
Remote Procedure Call.

RDBMS
Relational DataBase Management System.

RDO
Remote Data Objects. Microsoft technology for accessing databases. Overlays ODBC and is designed to access remote ODBC data sources. Superseded by ADO. 

Regression
The mathematical analysis of numerical data to identify a formula that best fits the trends in the data - often with the aim of successful prediction of future data.

Remove Sensing
The use of aerial and space imagery to record and interpret information.

RFC
Request for Comments

RFID
Radio Frequency Identification tags.

RIP
Routing Information Protocol. Allows a router to exchange routing information with other gateways and hosts. RIP versions:

RIS
Remote Installation Services. Enables administrators to install Windows 2000 professional on client computers throughout a network from a central location.

RMS
Windows Rights Management Service. 

ROFS
Read Only File System.

ROI
Return On Investment. ROI is traditionally regarded in terms of financial return, but it does also included staff moral, productivity and loyalty.

ROS
Remote Access Trojan. Trojan allowing an attacker to remotely access or control a computer.

Router
Network device connecting two networks that selectively forwards network packets according to their IP address. 

RPC
Remote Procedure Call.

RSA
A public-key encryption method. RSA is taken from the initials of the original authors of the RSA algorithm: Ronald Rivest, Adi Shamir and Leonard Adelman.

RSI
Repetitive Strain Injury. An general term for an injury caused by continual performance of repetitive tasks. Typically affecting either the hand, wrists, elbow or shoulder. Symptoms typically include pain and/or numbness.

RSL
(Windows) Registry Size Limit. This is the maximum size that (Microsoft) Windows will allow the registry to grow to.

RTOS
Real Time Operating System.

RTS
Request To Send. Used as part of serial hardware flow control.

RTTI
Run-Time Type Identification. Mechanism allowing the type of an object to be identified from a handle to its base type.

RUP
1. Rational Unified Process.
2. Restricted Use Product.

SAF
Server Application Function. An API for server software.

SAN
Storage Area Network.

SAP
Systems, Applications and Products in Data Processing. A leading ERP software package.

SAR
Segmentation and Re-assembly. Optional features of the Wireless Transport Protocol used to split large WTP messages into a number of smaller datagrams (with resend for failed datagrams), thereby improving the transmission efficiency of downloading large messages to a phone.

SCCS
Source Code Control System. An early version control system available on UNIX platforms. Widely regarded as having been superseded by rcs and cvs.

Schema
Oracle: The collection of database objects that are owned by a particular use are referred to as that user's schema. Every object in the database belongs to one and only one schema, and therefore, to one and only one user (although may still be accessed by many users).  

SCTP
Stream Control Transmission Protocol.

SDK
1. Software Development Kit.
2. Often taken to refer to Microsoft SDK.

SDTS
Spacial Data Transfer Standard. SDTS is a standard for the transfer of digital spatial data between (dissimilar) computer systems, with the potential for no information loss.

Seed point
A point (i.e. a location) against which information is tagged. Within a geographic area a seed point (which may also be referred to as its centroid) would have information associated with it about that geographic area.

SEM
Search Engine Marketing.

SEO
Search Engine Optimisation. The art of optimising a website so that it appears near the top of search engine search results.

SEP
Standby Emergency Power (power from emergency generators)

SERP
Search Engine Results Page(s).

Server Rooms
A concentration of file servers (computers)

Servlet
A Java server side module Servlets are platform-independent, 100% pure Java server-side modules that fit seamlessly into a Web server framework and can be used to extend the capabilities of a Web server with minimal overhead, maintenance, and support

SIP
Session Initiation Protocol. Used for setting up communications sessions on the internet, such as instant messaging, conferencing, telephony or whiteboarding.

SLA
Service Level Agreement.

SMART
Self Monitoring Analysis and Reporting Technology. A HDD diagnostic technology that monitors device performance and attempts to predict device failure. SMART software on the HDD monitors the internal performance of motors, media, heads and electronics of the drive. SMART software on the host monitors the overall reliability status of the drive.

SME
1. Small and Medium Enterprises.
2. Society of Manufacturing Engineers.

SMP
Symmetric Multi-Processing. The ability to run programs on the same machine but on different processors, all managed by the same operating system and sharing system resources such as memory, I/O, etc. Requires at least two processors.

SMS
Short Message Service - mobile phone text messaging.

SMTP
Simple Mail Transfer Protocol. A protocol for sending (or relaying) e-mail to a server. 

SOAP
Simple Object Access Protocol. A protocol that describes a model for packing XML enquiries and responses. SOAP messaging is used to enable exchange of a variety  XML information. The SOAP standard takes on the job of transporting service requests and replies between service users and service providers.

SOW
Statement Of Work.

SPAM
1. Unsolicited e-mail (or newsgroup posting) sent out in bulk, usually for commercial gain.
2. Variant on the above: Unsolicited bulk e-mail from a stranger. This definition distinguishes between spam and "opt in e-mail".

Spatial Query
Selecting objects based on their geometry.

SPI
Stateful Packet Inspection.

SPOT
Simple Personal Object Technology.

Strategi
Detailed digital map data providing a overview of geographical information on England, Scotland and Wales.

STS
Static Transfer Switch

SQL
Structured Query Language. Standard query language for retrieving, adding and updating information from database systems.

SQL Injection
An attack technique where an attacker tries to make an application execute unauthorised (or unintended) SQL.

SSI
Server Side Includes.

Standby Database
A standby database maintains a copy of a production database but in a permanent state of recovery. If the production database fails then the standby database can be opened (or promoted) with minimal recovery.

Struts
Struts is an open framework for designing Web applications. It helps users to develop application structures.

SVG
Scaleable Vector Graphic. An XML based language for describing two dimensional web graphics.

SW
Common abbreviation for software.

Switch Room
The main telephone switch serving the building

SWOT Analysis
Critical analysis of the Strengths, Weaknesses, Opportunities and Threats to a project.

Switch
Similar to a hub, in that it provides a central connection between two or more computers on a network, but with some intelligence. (A switch operates on Layer 2 (or above) of the OSI Layer 7 model and a hub operates at Layer 1.) Whereas for a hub any message received at the hub is broadcast to all the attached computers, with a switch it is sent only to the destination computer and is not visible to other attached devices. This does not prevent "broadcast" messages from being sent to all attached devices.

Synonym
A synonym is an alias for any table, view, snapshot, sequence, procedure, function or package contained within a database.

T&C
Terms and Conditions.

TAG/MRTD
Technical Advisory Group on Machine Readable Travel Documents.

TAPI
Telephony Application Programming Interface.

TAPI Server.
Microsoft definition: The central repository of telephony information on a user machine. This service process tracks local and remote telephony resources, applications registered to handle Assisted Telephony requests, and pending asynchronous functions, and it also enables a consistent interface with telephony service providers (TSPs).

On Windows 95, Windows 98, and Windows NT, TAPISRV runs as a separate service process. On Windows 2000, it runs within the context of Svchost.exe. When an application loads a TAPI DLL into its process space and performs an initialization operation, the DLL establishes an RPC link to the TAPI Server. The  TAPI  Server loads telephone service providers ( TSPs) into its process space. Regardless of how many applications access a given provider's devices, only one instance of a given TSP will exist.

TBD
1. To Be Done.
2. To Be Determined.

TBH
Shorthand for "To be honest".

TCP
Transmission Control Protocol.  Connection oriented protocol for establishing a connection between two computers and for managing the delivery of data packets between the those computers. TCP is often used in conjunction with IP, which it is referred to as TCP/IP.

TCPA
Trusted Computing Platform Alliance.

TCP/IP
Transmission Control Protocol/Internet Protocol. Transmission Control Protocol ( TCP ) used in conjunction with Internet Protocol (IP).

TD-1
Size 1 machine readable travel document; sizes specified by ISO 7810.

TD-2
Size 2 machine readable travel document; sizes specified by ISO 7810.

TDM
Time Division Multiplexing.

Thin client
1. A client/server application that is designed to minimize the amount of data (including the application itself) that needs to be transferred from the server to the client. Thin client applications are therefore small and perform most of the work on the server.
2. When applied to a computer rather than an application it refers to a client computer which is intended only to be used as a network client with no local storage and minimal processing capability. A thin client computer runs applications (such as word-processing, internet browser etc) on the server, using the thin client only as a display device. Thin client computers include network computers and X-terminals

TIGER
Topologically Integrated Geographic Encoding and Referencing System. Geographic and census information made available by the US Census Bureau.

TLA
Three Letter Acronym.

TLD
Top Level Domain.

TNS
Transparent Network Substrate. Oracle database networking interface technology that allows applications (notably SQL*Net) to communicate across a network. TNS maps requests through to the underlying networking technologies that are locally available.

TPC
Transaction Processing Council

TS
(Microsoft Windows) Terminal Server.

TS CAL
Terminal Server Client Access License.

TSP
Telephony service provider.

T-SQL
Transact-SQL. A set of extensions to standard SQL (derived from Sybase and Microsoft).

TWAIN
sThe TWAIN working group  is a non-for-profit organisation which represents the imaging industry, whose purpose is to provide and foster a universal public standard which links applications and image acquisition devices. TWAIN is often loosely referred to as an interface standard for image acquisition devices.

UAProf
Universal Agent Profile. Provides capability information about a WAP device. 

UBE
Unsolicited Broadcast E-mail. Unsolicited e-mail - otherwise more commonly known as spam. 

UCE
Unsolicited Commercial E-mail. Spam distributed with the aim of commercial gain.

UDDI
Universal Description Discovery and Integration. The specification for an index of all available Web services which is comparable to a global Yellow-Pages directory. UDDI helps businesses to produce descriptions of the services they offer, pass on details to the registry and thus appear to be a services provider. Using the UDDI method Web services users can send enquiries in the form of SOAP messages to the central registration point to ascertain suppliers of a particular service.

UDP
1. User Datagram Protocol. Like TCP, UDP sits above IP, but unlikeTCP it is aconnectionless communications protocol (meaning there is no handshaking between the sender and receiver). It provides a "best-effort" delivery, and neither the arrival or correct sequencing of datagrams is guaranteed. UDP is used by applications that do not require an acknowledgement and which send only small amounts of data.
2. Usernet Death Penalty.

UI
User Interface.

ULF
Universal Listener Framework. Works in the same way as a multi-protocol Web server. It works with browsers, monitors communication between applications and uses WAP mobile phones and other wireless devices. It consists of various pre-configured classes for receiving messages. An example of such a module is the FTP Listener. It receives incoming requests and passes them on to the ULF, which in turn transmits them through the firewall to the Total-e-Server.

UNC
Universal Naming Convention (or Uniform Naming Convention), for specifying the location of a resource on a network.

UP
Unified Process.

UPS
Uninterruptible Power Supply.

 USB
Universal Serial Bus. USB provides a single common interface to peripherals and plug-and-play configuration (at the host/pc). The original standard for USB (occasionally referred to as USB 1.0, but normally simply as USB) supported transfer speeds of 1.5Mbps and 12Mbps. USB 1.1 is a revised version of the USB specification, but the transfer rate remains unchanged. USB 2.0 (also referred to as "USB Hi-Speed) also supports 480Mbps and is otherwise backwards compatible with earlier versions.

User Authentication
The process of authenticating a user, i.e. of checking that a user is who they claim to be. Common user authentication is by means of a username and password (which authenticates the username), but can also included biometric checks such as fingerprint authentication or iris scan.

UTC
Coordinated Universal Time (UTC). It is the current term for what was commonly referred to as Greenwich Meridian Time  GMT).

Utility Power
Power from the local utility company

VA
Volt Amps. Used to measure the maximum load that can be placed on a UPS. VA = Maximum UPS load = Watts/0.7 = Amps x Voltage.

VB
(Microsoft) Visual Basic.

VB5
(Microsoft) Visual Basic - Version 5.

VB6
(Microsoft) Visual Basic - Version 6.

VBA
(Microsoft) Visual Basic for Applications.

VC
(Microsoft) Visual C++.

VCL
Visual Component Library. Component library supplied with Borland Delphi.

vcs
Version Control System. See also cvs, RCS, SCCS.

VDAP
Voice and Data Access Point.

VDS
1. Virtual Disk Services.
2. Virtual DMA Services.

VIZ
Visual Inspection Zone; areas (on a MRTD) which are not machine readable and are intended for visual (i.e. human) inspection only.

VLDB
Very Large DataBase.

VMS
VMS is an operating system from HP. It runs on both VAXs and Alphas - The VAX variant is known as "VAX/VMS" or "VMS VAX" and the Alpha variant is known as "VMS Alpha". The correct full name for VMS is " OPEN VMS". 

VoIP
Voice over IP.

VPE
1. Video Processing Engine.
2. Virtual Palm Encyclopedia.
3. Virtual Print Engine.
4. Video Port Extensions.
5. Visual Programming Environment.

VPN
Virtual Private Network. A virtual private network provides a secure connection between two or more computers across a public network (such as the Internet or a company LAN or  WAN) In a VPN data is encrypted between the participating computers - creating private "tunnels", ensuring that even were the data intercepted that it could not be read by any computer other than those participating in the VPN.

VRML
Virtual Reality Modeling Language.

VSS
1. (Microsoft) Visual Source Safe.
2. Volume Shadow-copy Service, also known as volume shadow copy. VSS takes a snapshot copy of a shared folder in order to make the shared folder available off-line - i.e. when the network connection to the shared folder is not available. VSS also records changes made to those files.

W2K
Microsoft Windows 2000 (workstation or server) operating system.

W3C
World Wide Web Consortium.

W95
Abbreviation for Windows 95.

W98
Abbreviation for Windows 98.

W9x
Abbreviation for Windows 95/98, sometimes also used to include Windows ME.

WAHO
Work At Home Opportunity. Alternative name for homework in some UK schools.

WAN
Wide Area Network. Typically much slower than a LAN. Typical speeds start at 56kbps. WANs typically provide connections between LANs that are at different geographical locations.

WAP
Wireless Application Protocol.

WBS
Work Breakdown Structure. The partitioning of a project into manageable units (or tasks) which can be individually planned, estimated and managed.

WBS Number
Number applied to an individual WBS unit or task to provide it with a unique identifying number.

WDDX
Web Development Data Exchange.

WEP
Wired Equivalent Privacy. Encrypts data at one end of a wireless link and decrypts it at the other end using either 64 or 128bit keys. Used to secure wireless networks. Normally incurs a slight hit on network speed.

WFS
Web Feature Service - for serving vector data in GML format.

WFW
Windows For Workgroups. Also known as Windows 3.11. Successor to Windows 3.1. Predecessor to Windows 95.

WGS84
Originally a military standard (MIL-STD-2401 Military Standard) produced to address the need for a global positioning coordinate system (for GPS). WGS84 is a earth fixed global reference frame used for defining coordinates when surveying and by GPS systems.

White List
List of approved or trusted people/vendors/items in the context of e-mail and Spam, a white list is a list of approved e-mail contacts that spam filtering software should allow through.

WIM
Wireless Identity Module or WAP Identity Module. A WIM identifies and authenticates a wireless device on a wireless network. It is normally (but not always) a tamper resistant device, such as a smart card.

WIN32
The Windows API for all 32 bit versions of windows, i.e. from Windows 95 onwards.

WINS
Windows Internet Name Service. Dynamic hostname based addressing scheme used on Microsoft LANs. Integrated with DNS, allowing WINS clients to resolve DNS names.

WLAN
Wireless LAN

WMI
Windows Management Instrumentation (W2K). Improves administrative control by allowing administrators to correlate data and events from multiple sources and vendors on a local or enterprise basis.

WMS
Web Map Service.

WNAP
Wireless Network Access Point. A network bridge, providing a connection for wireless devices to a fixed wired network.

WPA
Windows Product Activation.

WSDL
Web Services Description Language. An XML language which is used by service interfaces and protocol agreements, among others, for describing access to Web Services. WSDL is independent for the underlying service implementation language or component model.

WSFL
Web Services Flow Language. An XML language which describes how Web Services are composed. Thus examples taken from various Web Services can be specified, as can the way particular business objectives are able to be achieved by combining them. Typically the result is the description of a business process. The second possibility is describing communications samples taken from various Web Services. In this case the interactions of the various partners are depicted.

WTAI
Wireless Telephony Applications Interface.

WTL
Windows Template Library.

WTLS
Wireless Transport Layer Security.

WTP
Wireless Transport Protocol.

WTS
Web Terrain Service - for serving raster images of 3D views.

WWAN
Wireless Wide Area Network (Wireless-WAN.)

WYSIWYG
What You See Is What You Get. Normally applied to document or HTML editors that allow you to view the document while editing it as it will appear when printed or as a web page.

X.25
Packet switched data network protocol.
External Data Representation (library).

XML
Extensible Mark-up Language. Like HTML it is a specification for formatting web documents and web pages. It supports communication between various companies and applications. Despite the various operating system platforms and end devices, data access logic and application logic do not have to be changed.

XON 
Transmitter on. Used as part of flow control, it is a character transmitted to resume output from a sender.

XOFF
Transmitter off. Used as part of flow control, it is a character transmitted to suspend output from the sender.

XSL
Extensible Style-sheet Language. A language for converting and depicting XML documents which also transforms XML code into HTML code. In addition it filters and sorts XML data and can address various parts of an XML document. XML data are individually shown, with, for example, negative values represented in red. XML data supported by XSL can be transmitted to various end devices such as screens, printers or mobile phones.

YTD
Year To Date.