A-side and B-side originally referred to the two sides of gramophone records on which singles were released beginning in the 1950s. The terms have come to refer to the types of song conventionally placed on each side of the record, with the A-side being the featured song (the one that the record producer hopes will receive radio airplay and become a "hit"), while the B-side, or flipside, is a secondary song that often does not appear on the artist's LP.

The earliest 10-inch, 78 rpm, shellac records were single sided. Double sided recordings, with one song on each side, were introduced in Europe by Columbia Records and by the late 1910s they had become the norm in both Europe and the USA. There were no record charts until the 1930s, and radio stations (by and large) did not play recorded music until the 1950s (when top 40 radio overtook full-service network radio). In this time, A-sides and B-sides existed, but neither side was considered more important; the "side" did not convey anything about the content of the record.