Fusion is a shortening of jazz-rock fusion, a branch of jazz music. Until 1969, jazz was associated only with swing (and latin), and not with the straight rhytms, and electronic instruments of rock. In 1969, Miles Davis recorded Bitches Brew, the first fusion album, which incorporated straight rhythms, electric bass (until then only the upright bass was associated with jazz) and other 'rocky' elements. For example, in traditional jazz, the bass would almost invariably play a walking bass line, but in fusion, the bass would play more on the lines of riffs, on which improvisations could take place.

Noteworthy fusion performers:

Cream of fusion albums: There are lots of other good (and even great) fusion artists and albums. This is my pick, based on historical context, album sales and personal taste. If I inadvertently forgot something major, /tell me, it will be updated.