A B-side is literally the other side of a phonograph record, since records can have tracks pressed into both sides. Over time, however, the term “B-side” has come to be associated with specific connotations in the music industry, rather than the physical construction of record albums. B-sides are tracks which are unusual, rare, or secondary, deemed less important than the “A-side” songs, which are intended to be hits. Sometimes, the judgment about what should be marketed as an A-side and what should be marketed as a B-side is off, as evidenced by many B-sides which later became very popular.
In the early days of recording, not too much importance was attached to the A and B sides of a record. The shift began when record companies started putting the songs they felt would be hits on the A-side, with secondary songs and supplements on the B-side. Eventually, people began to associate “B-side” with the concept of a secondary track. The promotion of A and B sides was primarily for the convenience of radio stations and reviewers, with the goal of the record companies being the capture of the ear with the A side of the album.
B-sides may be variations on songs on the A-side, such as acoustic versions or remixes of a song. A B-side could also be a demo, a song which is not thematically related to an album, or a song which was unpolished at the time of the album's release. Since most recordings are not released on records today, B-sides are typically included on the single associated with a record, or marketed separately as the B-sides for a particular album.
Some artists and bands have collected and released all of their B-sides together, giving fans access to rare tracks along with a cohesive history of the band's style. B-sides may include bonus material like parody songs, covers of songs by other artists, and erratic material which didn't fit in with any of the artist's other releases. Some B-sides are designed to be rare, with a limited number being produced so that fans attach a high value to the bonus tracks.
Some notable B-sides have catapulted to fame. “Rain,” by The Beatles, for example, was a B-side when it was first released, along with “Don't Worry Baby” by the Beach Boys and “I Will Survive” by Gloria Gaynor. Many of the artists were surprised by the success of their B-side songs, which were tacked onto albums as afterthoughts.