Also music that is freely improvised. That is, music improvised outside the confines of a specific genre and without regard to any preconceived set of rules or organizing principles. Derek Bailey is one of the primary proponents of this sort of improvisation. There is often some overlap with jazz, such as Ornette Coleman, William Parker, et al. Other people who are, at times, free improvisers (in no particular order):

Fred Frith
Chris Cutler
Evan Parker
Davey Williams
LaDonna Smith
Eddie Prevost
Ikue Mori
Ruins/Tetsui Yoshida
Elliot Sharp