What is OGG?

Ogg is a completely free, open standard container format maintained by the Xiph.Org Foundation. This container format can multiplex a number of independent streams for audio, video, text (such as subtitles) and metadata.
The .ogg filename extension was used for all files whose content used the Ogg container format before 2007, but since 2007, it is only used for Ogg Vorbis audio file. Ogg has small size compared to a file in MP3 format because Ogg compression of digital audio varies in bit rate. The bit rate varies depending on the need, so the sound of silence will have a very small file size, or no size at all.
Because the format is free, and its reference implementation is non-copylefted, Ogg’s various codecs have been incorporated into a number of different free and proprietary media players.