From the article: Free Jazz and Free Improvisation: What's the Difference?
The term "jazz" can be highly contentious. It refers to so many styles of music that musicians and fans alike often find themselves in heated debates over which styles are included in the set of all things jazz, and what styles aren't. Even more fraught is the debate over free jazz and free improvisation. Are they mutually exclusive genres? Is either one really jazz? How do we define them?