one of the most common audio formats. The format was developed by Microsoft (in collaboration with IBM) and usually stores uncompressed audio data with pulse-code modulation, but it can be used to store sound processed with other audio codecs.
this format is free, which apparently is one of the reasons for its popularity. The used codecs supports variable bit rates (as a default), and .ogg files usually play back easily on all platforms. All things being equal, the sound quality exceeds that of mp3 somewhat.