Fusion Rock is a term used to describe the merging of Rock music with Jazz. Rock music has the four four beat, while Jazz introduces 6/8 and beyond, and uses music scales that go way beyond major or even minor and sevenths. Though suspended, diminished and augmented chords and other similar departures from your standard major chords, are in rock and roll tunes (the Beatles, especially), they are predominant in Rock that has "fused" with Jazz.
Weather Report, and the Mahivishnu Orchestra and even later endeavors by Miles Davis are examples of this.
Also, Ravi Shankar and John McLauglin joined forces in the studio, merging sitar and sizzling electric jazz guitar. Some R and B groups of the late 60's, like Michael Bloomfield's Long Time Comin' album with his Electric Flag ensemble swayed from the norm in their freedom musically.
The group Yes and Steely Dan (example: Aja) flirt very close to this genre.
Ironically, before Great Britain's Beatles tunefully invaded America, Georgie Fame and Blue Flames had a jazzy pop song, "I say Yeah, Yeah," that was not your regular four beat rock. Also I would like to mention Kyu Sakamoto's hit from Japan imported during the sixties, "Sukiyaki" (It sounded something like "Kee Oh Yo Fo Ya Ko Ro, Kee yo ray yo, Ka ra yo ya yo..." forgive my transliteration.) (And It reminds me when I almost became a Buddhist, but that's definitely another story!)
One should cite some other early tunes like Herb Albert's "The Lonely Bull,", Acker Bilk's work, and others' rock pop chart singles like the Dixieland inspired sounding "Midnight in Moscow."
Fusion Rock is probably too eclectic for being considered crossover music.
(See also Jazz-Fusion