Core X11 protocol client library

The X Window System is a network-transparent window system that was
designed at MIT. X display servers run on computers with either
monochrome or color bitmap display hardware. The server distributes
user input to and accepts output requests from various client
programs located either on the same machine or elsewhere in the
network. Xlib is a C subroutine library that application programs
(clients) use to interface with the window system by means of a
stream connection.