“Codec” stands for “Compression-Decompression algorithm.” In raw uncompressed form, multimedia files take up a huge amount of space. To minimise the space used, the multimedia video and/or audio files are encoded using a particular codec. When you want to listen to or view the file, a video/audio player decodes the information in the file using the specific compression-decompression algorithm. When a multimedia player (like Windows Media Player, Winamp, etc.) doesn’t play a particular file, the problem is usually that the required codec is missing.