What is X Windows?

The X Window System (commonly X, and sometimes informally X11 or X-Windows) is a windowing system for bitmap displays, common on Unix-like operating systems. It provides a framework and protocol for GUIs: it manages windows on a display, as well as keyboard and mouse input. Its widespread use allows applications to be run remotely, even across different architectures. X provides the basic framework for a GUI environment: drawing and moving windows on the screen and interacting with a mouse and keyboard. However, X does not mandate the user interface – individual client programs handle this.