n. (context music English) A style/sub-genre of hip hop characterized by hard-hitting drums, usually containing the kick drum/snare drum/hi-hat combination rather than claps, snaps, http://en.wikipedia.org/wiki/TR-8080 bass drums, cowbells, shakers, and various other percussion sounds used for rhythm.
Boom bap is a style of production in hip-hop music.
The term "boom bap" is an onomatopoeia for the drum sounds prominent in boom bap. It is usually recognized by an acoustic drum loop/break that is then chopped up and played using a sampler such as the Akai MPC and the SP1200.
In recent years the boom bap production style has made a slight comeback through artists such as Joey Bada$$, Pro Era and associated acts.