In the field of recorded music, a hidden track (sometimes called a secret track or ghost track) is a piece of music that has been placed on a CD, audio cassette, LP record or other recorded medium in such a way as to avoid detection by the casual listener. In some cases, the piece of music may simply have been left off the track listing, while in other cases more elaborate methods are used. In some rare cases a "hidden track" is actually the result of an error that occurred during the mastering stage of the record's production.