While swing music tended to feature orchestrated big band arrangements, bebop music highlighted improvisation. Typically, a theme (a "head," often the main melody of a pop or jazz standard of the swing era) would be presented together at the beginning and the end of each piece, with improvisational solos based on the chords of the compositions. Thus, the majority of a piece in bebop style would be improvisation, the only threads holding the work together being the underlying harmonies played by the rhythm section. Sometimes improvisation included references to the original melody or to other well-known melodic lines ("quotes", "licks" or "riffs"). Sometimes they were entirely original, spontaneous melodies from start to finish.