Ogg

Ogg is a format and file extension for audio files, and sometimes for video files (ogg Theora). It is an open source format, unlike Mp3 which is closed source.

The ogg format uses a lossy compression algorythm which affects the bit rate of a given source (usually wav files). The bit rate of a compressed ogg file is variable. For example, an ogg file with specifications "44100 Hz, 128 kbps" means that its bit rate is, on average, 128 kilobits per second; some pieces of the file with mostly low frequencies can be compressed at a lower bit rate without losing much precision, while others with mostly high frequencies are compressed less to avoid an excessive loss of detail.