An Acronym for Coder / Decoder.

In a communication systems the coder and decoder sit at the transmitter and receiver respectively and transform the stream from the internal encoding to an external encoding for transmission the back to the internal encoding at the other end. Encoder/Decoder pairs commonly insert perform exotic ErrorCorrection, synchronisation and timestamping features into the stream.

A Codec? is a library (or a set thereof) which encapsulates access to a certain data format (commonly audio or video). The term is usually used in relation to MediaPlayers, who commonly use Codec?s as interchangable backends to support various media formats. For example, to view DivX files on your computer you will need a DivX Codec? for your MediaPlayer.