"ReplayGain is a proposed standard published by David Robinson in 2001 to measure the perceived loudness of audio in computer audio formats such as MP3 and Ogg Vorbis."
From Wikipedia: ReplayGain:
ReplayGain is a proposed standard published by David Robinson in 2001 to measure the perceived loudness of audio in computer audio formats such as MP3 and Ogg Vorbis. It allows players to normalize loudness for individual tracks or albums. This avoids the common problem of having manually to adjust volume levels between tracks when playing audio files from albums that have been mastered at different loudness levels.
Although the standard is now formally known as ReplayGain,[1] it was originally known as Replay Gain and is sometimes abbreviated RG.
