Hidden track

In the field of recorded music, a hidden track (sometimes called a ghost track, secret track or 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 the result of an error that occurred during the mastering stage of the recorded media. Since the rise of digital and streaming services such as iTunes and Spotify in the late 2000s and early 2010s, the inclusion of hidden tracks has declined on studio albums.