X Recommendations
X Recommendations refers to a set of CCITT (now ITU-T) documents that describe data communication network standards. Well-known ones include X.25 Packet Switching standard, X.400 Message Handling System, and X.500 Directory Services.

X Terminal
X Terminal is an X Windows application that allows a user simultaneous access to several different applications and resources in a multi-vendor environment through the implementation of X Windows. Instead of transmitting vast amounts of X information over the data link, the server software is executed on the host system and eliminates the time-consuming data transfer. Sophisticated data compression techniques and an optimized protocol then send only the minimum amounts of display commands to the terminal. With minimal data being received, the processor and custom graphics engine within these powerful X Terminals are free to concentrate on decompressing drawing commands and maintaining error-free communications.

X Window System
X Window System is a distributed, network-transparent, device-independent, multitasking windowing and graphics system originally developed by MIT for communications between X terminals and UNIX workstations. It provides the standard toolkit and protocol to build graphical user interfaces (GUI) on Unix, Unix-like operating systems, and OpenVMS – almost all modern operating systems support it. X provides the basic framework for a GUI environment: drawing and moving windows on the screen and interacting with a mouse and/or keyboard.

X.25 Packet Switching
X.25 Packet Switching refers to the switching process between the data terminal equipment (DTE, a user machine) and the data circuit terminating equipment (DCE, a network component), using X.25 protocol. In a typical X.25 Packet Switching network, the major components are the customer premises equipment (CPE, e.g., user terminals or host computers), packet assemblers/Dis-assemblers (PADs), concentrators, and X.25 switches.

XE: TransPath Execution Environment
TransPath Execution Environment(XE) is a layer of software providing shared services for all application software on the TransPath and isolating higher-level software from operating system dependencies.

XID: Exchange Identification
Exchange Identification (XID) is the request and response packets exchanged prior to a session between a router and a Token Ring host. If the parameters of the serial device contained in the XID packet do not match the configuration of the host, the session is dropped.

XRemote
XRemote is a open source tool developed specifically to optimize support for the X Window System over a serial communications link. XRemote is a simple tool for controlling the mouse and keyboard of a remote X-server. The application grabs all local keyboard and mouse action and sends it to the remote X-server which repeats the same things.

XRM
XRM is an ATM Available Bit Rate (ABR) service parameter, which limits the number of forward RM-cells which may be sent in the absence of received backward PM-cells. The range is 0-255. For ABR traffic, Xrm effects the time rate of change of the ACR. This value effects TCP round trip time calculations, which in turn effects TCP throughput.

XStream
XStream is an open-source Java library for serializing objects into XML and deserializing that XML into objects. XStream relies on Java idioms such as object names to produce element names and strings within classes to produce element content. It also produces a kind of reflection of objects in XML.

Zero Code Suppression
Zero Code Suppression is a line coding scheme used for transmission clocking. Zero line suppression substitutes a 1 in the 7th bit of a string of eight consecutive zeros

ZIP Storm
ZIP Storm refers to the broadcast storm that occurs when a router running AppleTalk propagates a route for which it currently has no corresponding zone name. The route is then forwarded by downstream routers, and a ZIP storm ensues.

Zone AppleTalk
A zone, a concept in AppleTalk network, refers to a logic group of network devices that is defined when the network administrator configures the network. The nodes or networks need not be physically contiguous to belong to the same AppleTalk zone. An AppleTalk Zone is equivalent to a local TCP/IP subnet.

Zone H.323
Zone, in the H.323 VOIP network, is the collection of H.323 nodes such as gateways, terminals, and multipoint control units (MCUs) registered with the gatekeeper. There can only be one active gatekeeper per zone. These zones can overlay subnets and one gatekeeper can manage gateways in one or more of these subnets.

Zone Multicast Address
Zone Multicast Address is a data-link-dependent multicast address within the AppleTalk computer network protocol suite at which a node receives the NBP broadcasts directed to its zone.

Zone Prefix
Zone Prefix, a concept in the H.323 VOIP netowrk, is a prefix that identifies the addresses to be serviced by a given gatekeeper. Zone prefixes are typically area codes and serve the same purpose as the domain names in the H.323-ID address space.