A codec, which may alternately stand for "Coder-Decoder" or "Compressor/Decompressor", is a program that encodes and decodes data. Typically this refers to multimedia codecs such as [[XviD]] that can encode compressed [[MPEG-4]] video files and play them back again.

Codecs are typically divided into two categories: lossy and lossless. Lossy codecs, like [[Theora]] are codes whose encoding process strips data deemed unnecessary in favor of small file size. Lossless codecs, like [[FLAC]] on the other hand rely on algorithmic data compression to compress media without losing a byte of media quality.