What is a back beat?

Answer 1

When you talk about music, a backbeat means placing rythmic stress on the second and fourth beats of a measure. This means emphasizing the even beats in 4/4 time, while the first and third beats (the odd beats) are less weighted. A backbeat may go something like this: 1 2 3 4.

A nice sample is: Fats Domino "Ain't That a Shame"

Answer 2

in music, a backbeat is an accent on the second and fourth beats of music in 4/4 time.