Hidden Track
A hidden track can be three things:
a track that is not listed on the release's sleeve (→UntitledTrackStyle).
a song in the pregap of track 1 on a CD, i.e. is located before the first track (a so-called PregapTrack) (→NonAlbumTrack, case 3).
one or more songs that follow another song on the same track, usually after a longer period of silence, but are not listed on the sleeve (→UntitledTrackStyle & MultipleTitleStyle).
Hidden tracks follow UntitledTrackStyle.