X11

The X Window System (X11, or shortened to simply X) is a windowing system for bitmap displays, common on UNIX-like computer operating systems. X provides the basic framework for a GUI environment: drawing and moving windows on the display device and interacting with a mouse and keyboard. X does not mandate the user interface – this is handled by individual programs. As such, the visual styling of X-based environments varies greatly; different programs may present radically different interfaces.

X11