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.
References
Boom bap Wikipedia(Text) CC BY-SA