Backbeat (or back beat) is the accentuation of beats 2 and 4 of a bar in 4/4 time (i.e. the 'off' beats).

 

In other common time signatures, the backbeat will land elsewhere. For example, the backbeat lands on 4 and 10 in 12/8 time.

 

Backbeat is a common rhythmical feature of most contemporary pop music, including rock, as the loud snare drum falls on these beats. Reggae, in particular, places emphasis on the backbeat.