X.25

X.25 is an ITU-T standard protocol suite for packet-switched data communication in wide area networks.

X.400

X.400 is a suite of ITU-T Recommendations that defines the ITU-T Message Handling System.

XAUI

10 Gigabit Attachment Unit Interface, is a standard for extending the XGMII between the MAC and PHY layer of 10 Gigabit Ethernet defined in Clause 47 of the IEEE 802.3 standard.

XDR

Extended Detection and Response, is a new approach to threat detection and response that provides holistic protection against cyberattacks, unauthorized access and misuse.

xDSL

Refers collectively to all types of Digital Subscriber Lines, the two main categories being ADSL and SDSL. Two other types of xDSL technologies are High-data-rate DSL (HDSL) and Very high DSL (VDSL).
DSL technologies use sophisticated modulation schemes to pack data onto copper wires. They are sometimes referred to as last-mile technologies because they are used only for connections from a telephone switching station to a home or office, not between switching stations.
xDSL is similar to ISDN inasmuch as both operate over existing copper telephone lines (POTS) and both require the short runs to a central telephone office (usually less than 20,000 feet). However, xDSL offers much higher speeds - up to 32 Mbps for downstream traffic, and from 32 Kbps to over 1 Mbps for upstream traffic.

XGMII

10 Gigabit Media Independant Interface.

XHTML

Extensible Hypertext Markup Language, a hybrid between HTML and XML specifically designed for Net device displays. XHTML is a markup language written in XML; therefore, it is an XML application. XHTML uses three XML namespaces (used to qualify element and attributes names by associating them with namespaces identified by URI references. Namespaces prevent identically custom-named tags that may be used in different XML documents from being read the same way), which correspond to three HTML 4.0 DTDs: Strict, Transitional, and Frameset. XHTML markup must conform to the markup standards defined in a HTML DTD. When applied to Net devices, XHTML must go through a modularization process. This enables XHTML pages to be read by many different platforms. A device designer, using standard building blocks, will specify which elements are supported. Content creators will then target these building blocks--or modules. Because these modules conform to certain standards, XHTML's extensibility ensures that layout and presentation stay true-to-form over any platform.

XLink

XML Linking Language.

XML

Short for Extensible Markup Language, a specification developed by the W3C. XML is a pared-down version of SGML, designed especially for Web documents. It allows designers to create their own customized tags, enabling the definition, transmission, validation, and interpretation of data between applications and between organizations.
Whether XML eventually supplants HTML as the standard Web formatting specification depends a lot on whether it is supported by future Web browsers. Microsoft Internet Explorer version 5 handles XML, but renders it as CSS, and Mozilla (Netscape) is still experimenting with XML support.

Xmodem

Originally developed in 1977, Xmodem is one of the most popular file-transfer protocols. Although Xmodem is a relatively simple protocol, it is fairly effective at detecting errors. It works by sending block of data together with a checksum and then waiting for acknowledgment of the block's receipt. The waiting slows down the rate of data transmission considerably, but it ensures accurate transmission. Xmodem can be implemented either in software or in hardware. Many modem, and almost all communications software packages, support Xmodem. However, it is useful only at relatively slow data transmission speeds (less than 4,800 bps).
Enhanced versions of Xmodem that work at higher transmission speeds are known as Ymodem and Zmodem.

XPointer

XML Pointer Language.

XSL

Extensible Style Language, a specification for separating style from content when creating HTML or XML pages. The specifications work much like templates, allowing designers to apply single style documents to multiple pages. XSL is the second style specification to be offered by the World Wide Web Consortium (W3C). The first, called CSS, is similar to XSL but does not include two major XSL's innovations -- allowing developers to dictate the way Web pages are printed, and specifications allowing one to transfer XML documents across different applications. W3C released the first draft of XSL in August 1998, and promotes the specifications as helpful to the Web's speed, accessibility, and maintenance.

XSLT

Extensible Style Language Transformation, the language used in XSL style sheets to transform XML documents into other XML documents. An XSL processor reads the XML document and follows the instructions in the XSL style sheet, then it outputs a new XML document or XML-document fragment. This is extremely useful in e-commerce, where the same data need to be converted into different representations of XML. Not all companies use the exact same programs, applications and computer systems.

XY Plotter

A XY plotter, also referred to as a pen plotter, is a computer-controlled machine that draws graphics or text with incredible speed and precision. An image is created by one or more writing implements, which are raised, lowered, and moved over the printing media to draw.