X

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X is the short form for the X Window System (commonly X11 or X) and it is a windowing system which implements the X display protocol and provides windowing on bitmap displays. It provides the standard toolkit one needs in order to build graphical user interfaces (GUIs) on most Unix-like operating systems, and has been ported to many other contemporary general purpose operating systems.

X provides the basic foundations and general framework for building GUI environments. It provides the platform for drawing and moving windows on the screen and interacting with a mouse and/or keyboard.

X was originally created at MIT in 1984.