The X Window System (X11, or simply X) is a windowing system for bitmap displays, common on Unix-like 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.

What are some examples of windowing systems?

Commercial systems such as Microsoft Windows (XP, 9x and earlier), the classic Mac OS (version 9 and earlier), and Palm OS, contain a windowing system which is integrated with the OS.

What is the X11 protocol?

X11 is a remote-display protocol used by Linux/Unix machines, including the Linux machines at Thayer. By running an X11 program (known as a server) on your computer, you can access graphical Linux programs remotely through an SSH client.