Bop, also called bebop, is a modern jazz style characterized by rhythmic and harmonic complexity, improvised solo performances (see also scat), and a virtuoso execution. It was pioneered in the early forties by alto saxophonist Charlie Parker, pianist Thelonious Monk, trumpeter Dizzy Gillespie, and others. Bop was usually played by small combos of musicians with a great amount of technical facility.