When referring to
audio codecs,
Variable bit rate (
VBR) encoding varies the compression in each time segment (usually one second), based on the complexity of the sounds to be compressed. The goal being to get the best balance between sound quality and compression possible at any given moment.
Formats such as Ogg Vorbis are inherently VBR. MP3s can optionally being encoded in this way.
See also constant bit rate[?].