Ogg is a digital multimedia container format designed to provide for efficient streaming and manipulation of digital multimedia. It is maintained by the Xiph.Org Foundation and is free and open, unrestricted by software patents. Its name is derived from "ogging", jargon from the computer game Netrek.
The Ogg container format can multiplex a number of independent streams for audio, video, text, and metadata. In the Ogg multimedia framework, Theora provides a lossy video layer. The audio layer is most commonly provided by the music-oriented Vorbis format or its successor Opus. Lossless audio compression formats include FLAC, and OggPCM.
Until 2007, the .ogg filename extension was used for all files whose content used the Ogg container format. Since then, the Xiph.Org Foundation recommends that .ogg only be used for Ogg Vorbis audio files. From Wikipedia
