A-side and B-side are words used in music. They used to mean the two different side of 7 inch vinyl records. Singles were released on these from the 1950s. The words now mean the types of song that are usually placed on each side of the record. The A-side is normally the featured song. This is the one that the record producer hopes will receive radio airplay and become a "hit". The B-side, or flipside, is a secondary song that often does not appear on the artist's LP.
A-side and B-side Facts for Kids. Kiddle Encyclopedia.