X features network transparency, which means an X program running on a computer somewhere on a network (such as the Internet) can display its user interface on an X server running on some other computer on the network. Unlike most earlier display protocols, X was specifically designed to be used over network connections rather than on an integral or attached display device.

As such, the visual styling of X-based environments varies greatly different programs may present radically different interfaces. Programs may use X's graphical abilities with no user interface. X does not mandate the user interface individual client programs handle this. X provides the basic framework, or primitives, for building such GUI environments: drawing and moving windows on the display and interacting with a mouse, keyboard or touchscreen. In its standard distribution it is a complete, albeit simple, display and interface solution which delivers a standard toolkit and protocol stack for building graphical user interfaces on most Unix-like operating systems and OpenVMS, and has been ported to many other contemporary general purpose operating systems. Each person using a networked terminal has the ability to interact with the display with any type of user input device. X is an architecture-independent system for remote graphical user interfaces and input device capabilities. The X.Org Foundation leads the X project, with the current reference implementation, X.Org Server, available as free and open-source software under the MIT License and similar permissive licenses. The X protocol has been at version 11 (hence 'X11') since September 1987. X originated as part of Project Athena at Massachusetts Institute of Technology (MIT) in 1984. X does not mandate the user interface – this is handled by individual programs. X provides the basic framework for a GUI environment: drawing and moving windows on the display device and interacting with a mouse and keyboard.

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

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