The word codec may be a combination of any of the following: 'Compressor-Decompressor', 'Coder-Decoder', or 'Compression/Decompression algorithm'.
An audio codec is a computer program that compresses/decompresses digital audio data according to a given audio file format or streaming audio format. Most codecs are implemented as libraries which interface to one or more multimedia players, such as XMMS, Winamp or Windows Media Player.
A video codec is a device or software that enables video compression and or decompression for digital video. The compression usually employs lossy data compression. Historically, video was stored as an analog signal on magnetic tape. Around the time when the compact disc entered the market as a digital-format replacement for analog audio, it became feasible to also begin storing and using video in digital form, and a variety of such technologies began to emerge.