What are rhythm charts for?

The rhythm charts are for drummers, as well as keyboards and guitars. It doesn't give notes, just beats and rhythms. It is slash notation, formally called 'Comping'.As Wikipedia describes: Comping (an abbreviation of accompanying) is a term used in jazz music to describe the chords, rhythms, and countermelodies that keyboard players (piano or organ) or guitar players use to support a jazz musician's improvised solo or melody lines.