Coined by Ornette Coleman; it was the title of one of his albums. It's jazz improvisation, but without a fixed rhythmic or harmonic basis for those improvisations - this was a radical change from previous eras of jazz. Also, the early-jazz ("Dixieland") notion of collective improvisation was reintroduced. This led, in time, to a more genre-less genre called free improvisation.
There were actually two improvisations recorded by the double quartet for Ornette's Free Jazz LP December 21, 1960; one just happened to be, at 17 minutes running time, enough to fit onto a side of vinyl -- presumably that was Plan B. The actual release, in 1961, consisted of the second, 35 minute, take, split into two parts/sides via a fade. The original take was released (as "First Take") on Twins (1971, reissued 1982), one of several Atlantic Records' 70's/80's collections of from-the-vaults Ornette from '59-'61.
The quartet of Coleman, Don Cherry, Scott LaFaro, and Smiling Billy Higgins are in one stereo channel, Eric Dolphy, Freddie Hubbard, Charlie Haden, and Ed Blackwell are in the other channel. I'd like to hear this remixed for surround sound, but since it was recorded before the days of multimultitrack recording, it may take a bit of filtering legerdemain to pull that off.
NOTE: The CD contains both takes. Damn well better, for what one has to pay these days... | 
