Chordal accompaniment, thatís the stuff that guitarists and pianist do when someone else is playing the melody or soloing. Itís often not given much focus, but is the stuff that can make or break a tune. The Jazz term for this is comping short for accompaniment.
Lets start with a look at some guitar chord terminology which may help with explanation
Early jazz - No Guitar Banjo
Most of the first Jazz Guitarists started out on Banjo