B-side Definition
bēsīd
noun
The side of a phonograph single opposite the side containing the featured performance; flip side.
Webster's New World
The recording contained on this side.
Webster's New World
An extra recording released along with a featured performance, as on a CD.
Webster's New World
Any song included on a compact disc single, besides the first song (the A-side).
Wiktionary
Other Word Forms of B-side
Noun
Singular:
B-side
Plural:
b-sidesOrigin of B-side
From the B on the record's label
From American Heritage Dictionary of the English Language, 5th Edition