X Window is called X11 in version 11. Normally, the release version is appended to the name, for example X11R6 for version 6.
X11 is a network-compatible system for the effective presentation of graphical user interfaces for Unix systems. X11 supports program exchange in client-server architectures between X clients and X servers, where the X server provides all the resources for data input and the client is the application program used to perform the computation of the data. The client and servercommunicate using the X protocol.
X11 relies on Windows managers to create a corresponding desktop environment such as K-Desktop-Environment, Gnome or FluxBox. X11 was developed in 1984 by the Massachusetts Institute of Technology (MIT) and licensed under MIT licenses. The current version is X11R7.5.