A-side and B-side
The A-side and B-side are the two sides of phonograph records and cassettes, and the terms have often been printed on the labels of two-sided music recordings. The A-side usually features a recording that its artist, producer, or record company intends to receive the initial promotional effort and radio airplay and hopefully become a hit record. The B-side (or "flip-side") is a secondary recording that typically receives less attention; although some B-sides have been as successful as, or more so than, their A-sides.