"Comping" (derived from the word accompany) is an expression used to describe playing rhythm back-up (playing chords) while another instrument solos.
Comping may be simple (as in four to the bar playing discussed in the following), or rhythmically complex. As you learn more about harmonized scales, chord substitution, 3 note chords etc., your comping style will improve.
Remember the simplest comping style can sometimes be the most effective.