A graphical user interface (or GUI, often pronounced "goo-ee") is a method of interacting with a computer that uses graphical images and widgets in addition to text.
The graphical user interface was invented at Xerox PARC and most modern general purpose GUIs are derived from it. (Some say GUIs were conceptualized by Doug Engelbart and first created by Xerox.) For this reason some people call this class of interface a PARC User Interface (PUI). The PUI consists of graphical widgets such as windows, menus, buttons, radio boxes, and icons, and employs a pointing device (such as mouse, trackball, or touchscreen) in addition to a keyboard. For this reason, many people refer to PUIs as WIMPs (Windows, Icons, Mouse, Pointer). Widgets are often pre-implemented in the form of widget toolkits.
Examples of systems that support PUIs are Mac OS, Microsoft Windows, and the X Window System. The latter is extended with toolkits such as Motif (CDE), Qt (KDE), GTK+ and (GNOME).
GUIs that are not PUIs are most notable in computer games. Advanced GUIs based on virtual reality are frequent in research.
There also exist GUIs which are designed for vertical market segments. These are known as application-specific GUIs. One example of such a GUI is the now familiar touchscreen point of sale software found in restaurants worldwide. First pioneered by Gene Mosher on the Atari ST computer in 1986, this touchscreen GUI has spearheaded a worldwide revolution in the use of computer technologies throughout the food & beverage industry and in the retail segment in general.
Similar to GUIs are text user interfaces (TUIs) that display the same types of widgets in a character-cell mode rather than in a pixel mode. Examples include the interfaces of many ncurses and MS-DOS applications.
The graphical user interface is generally contrasted with the command line interface (CLI).
Because GUIs and TUIs tend to show most or all relevant categories of commands on the display, users often learn them faster than CLIs, but users with vision or motion disability often have trouble navigating in a GUI, and most commercial GUIs use at least an order of magnitude more computer power than a CLI, making a GUI unwieldy on older hardware.
See also: History of the GUI, UIML, Fitts' law, Anti-Mac, Apple v. Microsoft