Also known as Coltrane Matrix, Coltrane Cycle, chromatic third relations, and multi-tonic changes.
What are the Coltrane Changes? What's the theory behind them? How are they used in improvisation, harmonization, and reharmonization?
Look up "Coltrane changes" in wikipedia.org. Essentially, they consist of a minor third interval followed by a perfect fourth interval (e.g. B-D-G-Bflat, etc.). Coltrane's compositions "Giant Steps" and "Countdown" are good examples, as well as his changes on the bridge of his recording of the standard "Body and Soul". The wikipedia article explains this in considerable depth.