Beat is a unit of musical time; when you tap your foot to music, each tap is a beat. Beat is not a particularly technical term, and has no formal definition. If two people tap their feet to the same music but one taps twice as fast as the other, neither is wrong; they simply take different note-values as their unit of time.

Much music is characterised by a sequence of stressed and unstressed beats organised into a time signature, the speed of which is determined by a tempo. In the context of a time signature, the term "beat" most often means the denominator; so in 3/4, most people would consider the beat to be the 4, that is, a quarter-note or crotchet.

Musicians, however, typically find that mentally counting a regular series of beats enables them to keep synchronised even if the music is not characterised by regular rhythm.