WAN
Wide Area Network

WAS
Web Attached Storage

WATS
Wide Area Telephone Service

WCDMA
Wireless Code Division Multiple Access

WDM
Wavelength Division Multiplexer

WEP
Wired Equivalent Privacy

WFQ
Weighted Fair Queuing - Cisco ¨

WLAN
Wireless Local Area Network

WRR
Weighted Round Robin - Cisco ¨

WTA
Wireless Telephony Access

WTLS
Wireless Transport Layer Security

WWW
World Wide Web

W3C
World Wide Web Consortium

WYSIWYG
What You See Is What You Get

X

X.21
The X.21 interface was recommended by the CCITT in 1976. It is defined as a digital signaling interface between customers - DTE - equipment and carrier's equipment - DCE - And thus primarily used for telecom equipment.
All signals are balanced. Meaning there is always a pair (+/-) for each signal, like used in RS422. Electrically the X.21 signals are the same as RS422, so please refer to RS422 for the exact details.

X.25
A CCITT X-Series Recommendation concerning protocols for OSI layers 1, 2, and 3, governing connections to public data networks. A series of widely adopted recommendations governing connections to packet switching networks using virtual circuits 
X.25 Cause and Diagnostic Codes
International Problem Diagnostic Code Differences 

X.28
A CCITT recommendation that defines the terminal-PAD interface.

X.400
A CCITT recommendation specifying a standard for electronic mail transfer.

X.500
A CCITT recommendation specifying a standard for distributed maintenance of files and directories.

XNS
Xerox ¨ Network Services

XOT
X.25 Over TCP-IP - RFC 1613


XTP
Express Transport Protocol

XUL
eXtensible User Interface Language. Language based on XML which describes the component of a user interface.

Y

Y-MODEM
Error-free file transfer protocol that can be used on error-corrected links and to transfer multiple files with a single command.

Z

ZBTSI
Zero Byte Time Slot Interchange

ZIP
Zone Information Protocol

Z-MODEM
Error free file transfer protocol that supports multiple file transfers, plus many other advanced features.