In the field of recorded music, a hidden track (sometimes called a ghost track or a secret track or an unlisted track) is a song or a piece of audio 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 rare cases a 'hidden track' is actually the result of an error that occurred during the mastering stage production of the recorded media.