Bass drum
A large, heavy drum that produces a low-pitched (but untuned) "thump". It is used in marching music and throughout 20th century popular music.
It is used to punctuate time. In marches it is used to keep the march even (marching bands march to the beat of the bass). A basic beat for rock and roll has the bass drum played on the first and third beats of a bar of common time, with the snare drum on the second and fourth "back beats".