Four Character Code. Four letters that tell Windows which codec the video stream contained in an AVI file is encoded with (e.g. DIV5, HFYU, XVID etc.)

codec (compression) identifier Detailed description

A four character code that uniquely identifies a video data stream format. A video player will look up the FourCC code then look for the codec associated to the code in order to play the associated video stream. This idea was used in the IFF multimedia format developed by Electronic Arts for the Amiga in the early 1980s. This file format was copied by Apple (who called it AIFF) and Microsoft (RIFF). Almost Definitive FourCC List

A four-character code identifying the format of a video stream. In order to play the video, the video player needs to find the FourCC code associated with it and then find the appropriate codec.