Comping is the accompaniment that a pianist, guitarist or organist provides behind a soloist or singer. The word is generally explained as short for “accompanying”, and possibly also linked to “complementing”. It is not a fixed part: the player chooses chord voicings, often rootless because the bass already supplies the root, and places them in irregular, conversational rhythms, leaving space when the soloist is busy and pushing when the music builds. Drummers comp too, with snare and bass-drum accents under the steady ride cymbal.
Good comping sounds simple but requires constant listening, since it shapes the energy of every solo. Many jazz lo-fi tracks are, in effect, extended comping: a few bars of soft electric-piano or guitar chords, either sampled or played, repeated under a beat, with occasional melodic fragments floating above.