X
X client
A program that uses the X server's services, including applications programs, which may run either on the same machine or elsewhere on the network. The GUI itself is a client.
X display
A keyboard, mouse and one or more screens.
X font
A file in the X Window System that contains the electronic character descriptions for a particular font. An X font is a bitmapped font and cannot be created or edited in the Outline Font Editor.
Xlib
A C library of about 300 low-level X commands at the heart of the X Window System. Xlib commands do things like draw lines, open and close windows, fill polygons, and track the mouse and other user events. It is possible to write X applications completely from Xlib commands (just as it is possible to write complicated software in Assembler), but it is easier to use higher-level commands, such as those in various Xtoolkits.
XNP
X Network Protocol. A high-level protocol that defines data structures for communicating between clients and servers.
X server
The X program that manages the display and runs locally on the terminal or computer on the desktop.
Xtoolkit or Xt Intrinsics
Any subroutine library that contains higher-level mechanisms than Xlib for generic tasks like drawing window borders, scroll bars, and buttons.
X Window System
A standard method of handling displays that can be used to build a windowing environment. Two popular GUI's, Motif and OpenLook, have been built on the X standard.
X-Y digitizing tablet
A peripheral device for manually translating line and point data (like engineering and technical drawings) into some computer format (usually vector or CAD). The drawing is secured to the tablet, and the operator positions the device's cursor (which may look like a pen or a computer mouse with a crosshair lens) over lines and other elements, clicking a button or pressing a key to record a coordinate.