In music, a single is a type of release, typically a song recording of fewer tracks than an LP record or an album. One can be released for sale to the public in a variety of formats. In most cases, a single is a song that is released separately from an album, although it usually also appears on an album. In other cases a recording released as a single may not appear on an album. Historically, when mainstream music was purchased via vinyl records, singles would be released double-sided, i.e. there was an A-side and a B-side, on which two songs would appear, one on each side.