Free jazz
Previous jazz forms used harmonic structures, usually cycles of diatonic chords. When improvisation occurred, it was founded on the notes in the chords. Free jazz almost by definition is free of such structures, but also by definition (it is, after all, "jazz" as much as it is "free") it retains much of the language of earlier jazz playing. It is therefore very common to hear diatonic, altered dominant and blues phrases in this music.