The backbeat is the emphasis on the second and fourth beats of a bar in 4/4 time, rather than on the first and third. In most pop, rock, soul and hip hop the snare drum supplies it, while the kick drum takes the first beat: count “one, TWO, three, FOUR” and the capitals are where the snare hits. Clapping along on two and four rather than one and three is a common sign of a feel for the backbeat.
In swing-era and later jazz, drummers often mark beats two and four with the hi-hat pedal while the ride cymbal keeps the swing pattern. Boom bap and lo-fi hip hop place a relaxed snare or rimshot on the backbeat, often slightly late, to create their characteristic head-nodding motion; in jazz lo-fi the snare may be softened, filtered or replaced by a brush sound.