Ogg Media (OGM), meaning Ogg Media File, is a container format (for video, audio and subtitle streams). It was developed by Tobias Waldvogel and can do a few things the common AVI format cannot. OGM's features include in particular:
Chapter support
Multiple subtitle tracks
Multiple audio tracks of various formats (MP3, AC3, AAC, Vorbis, LPCM)
Vorbis audio support (there is no "correct" way for AVI to support Vorbis, making any attempt potentially incompatible and unreliable)
OGM support for Windows (Including Microsoft's Windows Media Player) is available via Tobias's own OggDS, Haali Media Splitter, VLC, or RadLight's Ogg Media filters (the last of which can also decode Theora video). On Unix-based systems OGM support is available in MPlayer, xine and VLC.Fundamentally, the format is a hack of the Ogg container format, which had only been designed to support encoders endorsed by Xiph.org ( website), the creators of Ogg. It is most likely going to be viewed as a temporary sol
Source:
http://en.wikipedia.org/wiki/OGM