Acronym for Graphical User Interface.

A GUI provides a graphical way of looking at data and normally involves the WIMP paradigm.

In MicrosoftWindows the GUI with all of its layers is built right into the OperatingSystem. Conversely, Linux has no provisions for GUIs of its own - it is provided by ordinary applications, commonly the XFree86 implementation of the X11 standard. This in turn is only a bare skelleton for GUIs which a large variety of DesktopEnvironments are built on top of. The most common ones are GNOME or KDE but there are more, such as XFce. Purists use X11 only to run multiple copies of xterm(1).

Note that a GUI does not necessary entail graphics mode; you can write console GUI applications using Curses.

Contrast CommandLine.