GUI
From APIDesign
Graphical user interface is the classical user interface (UI) people deal with when using desktop applications.
A GUI application is like a server-side application which is listening on thousands of ports at the same time, and responds differently not only to what messages are sent to what ports, but the order in which that happens. But moreover, server-side programming tends to be about objects with a well-defined lifecycle (session, request, etc.). The closest a GUI application has to that is the AWT event queue, and there are thousands of events a minute.
-- Tim Boudreau, Jan 25, 2010