Those not familiar with the term B-side have to go back to the vinyl recording days. Singles were 45 RPM records that on their A-sides usually had a cut from a band's newly released album. Because singles had two sides, the B-sides often had a less known track that didn't appear on the album. Although the B-sides didn't (with some exceptions) achieve the popularity of the tracks on the A-sides, they were more or less bonus material and highly sought after by collectors.