SWF, short for Shockwave Flash and pronounced "swif" is an open file format that was created and developed by Macromedia. Adobe then purchased Macromedia and SWF is available from the acquiring company now.
The format was created to be small enough to publish animations and vector graphics on the Internet and for the most part does so. SWF is occasionally used to create .gifs and menus for DVD movies, as well as television commercials.
Initially limited to simple vector based objects and images, newer versions allow for much more intense interactions with the end user including audio and video. SWF files can be played using Adobe Flash Player either through the standalone program, or as a browser plug-in in Internet Explorer, Firefox, Safari or Opera.
The format is so popular that according to an independent study conducted by Millward Brown, 99 percent of all web users have the plug in installed.
More recently, as of May 1st 2008, Adobe dropped all licensing restrictions on the format specifications making the format open for other developers.