Originally, the other, not-usually-
played side of a 78-rpm phonograph record. From way back in the
day, whenever it was that two-sided phonograph records became
popular.
Let's hear the
flip side of that record.
As '50's slang: You turn my record over, baby. Like, on the *
flip* side. (See "flip out" = "go crazyover, freak out over, be turned on by someone or
something.")