WIMP stands for Windows, Icons, Menus and Pointers (or maybe Windows, Icons, Mouse, Pull-down menus).
WIMP is the style of graphical user interface that uses the above-mentioned common widgets. It was invented at Xerox PARC, popularised by the Apple Macintosh and now available in other varieties such as the Microsoft Windows operating system, the X Window System, OSF/Motif, NeWS and RISC OS.
WIMP is also sometimes said to be a paradigm for human-computer interaction. It can, however, not be said to be an "interaction style" (see this).
Shneiderman, Ben (1997): Designing the User Interface: Strategies for Effective Human-Computer Interaction. (3rd ed.). Boston, MA, Addison-Wesley Publishing
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Free On-line Dictionary of Computing, Edited by Denis Howe(Original database files available at foldoc.org). [Accessible online]