To me, I think it means the faithful (to the extent possible) reproduction of the recording. Given that the recording is the music is presented to your system, I don't know what else it could mean. It is the absence of artifacts that can produce top end glare, which some hear as detail and may actually enjoy. Its also the absence of the sweet or veiled sound that some systems produce that some may enjoy, but is a departure from the music.
Beyond that, I think its one of the many audiophile terms that have no universal definition-audiophiles tend to backfit these terms to match what they like-or don't.

