X WIndow System

X

X is the shortened form of X-11 or X Window System which is a client-server protocol which was developed at MIT circa 1984. X provides the graphical user interface (GUI) on UNIX and Linux systems and has the additional benefit of having been designed to use Internet Protocol for transport of data. This means that the X protocol can be used over a network. When used over a network, X provides the means to create a remote desktop session, allowing a remote user to run a the computer providing the X session as if he were sitting at the computer.

Please note that it took Microsoft 20 years to develop the same 'remote desktop' capability for their "Windows" Operating Systems.
--InetDaemon