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 actually the result of an error that occurred during the mastering stage production of the recorded media. However, 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. It is occasionally unclear whether a piece of music is 'hidden.' For example, "Her Majesty," which is preceded by fourteen seconds of silence, was originally unlisted on The Beatles' Abbey Road but is listed on current versions of the album. That song and others push the definition of the term, causing a lack of consensus on what is considered a hidden track. Alternatively, such things are instead labeled as vague audio experiments, errors, or simply an integral part of an adjacent song on the record. Techniques A vinyl record may be double-grooved, with the second groove containing the hidden tracks. Examples of double-grooving include Monty Python's 'three-sided' Matching Tie and Handkerchief, Tool's Opiate EP, and Mr. Bungle's Disco Volante. Grooves cannot be read from digital media such as compact discs, so alternate methods were conceived. With a similar aim of concealment, unlisted tracks are sometimes given their own separate index point on digital media. Songs can be placed in the pregap of the first track of certain CD formats, so that the CD must first be cued to the track, and then manually back-scanned. These are often referred to as Track 0 or Hidden Track One Audio (HTOA). A CD player will not play these tracks without manual intervention, and some models (including many computer operating systems) are unable to read such content. On Super Furry Animals' third studio album, "The Citizens Band" is found in the pre-gap approximately five minutes before the beginning of track one. A glossary of terms used in the song's lyrics are printed on the interior of the cardboard outer sleeve