X clientAn application process in the X Window System. It gains access to windowing services via the Xlib library. These are translated by the system into X protocol messages to an X server.
Xbase ♦ xbeeb ♦ xbm ♦ XC ♦ X client ♦ X Consortium ♦ Xcoral ♦ xdbx ♦ X-Designer
Try this search on Wikipedia, Wiktionary, Google, OneLook.