Called "jazz-
rock fusion" or "electric jazz" when it became a phenomenon in the late-
60's/early-
70's. Nowadays referred to as "fusion". Origins: the twin rises of
The Beatles and
soul music; musicians started including a backbeat on tunes.
Gary Burton and
Larry Coryell, et al, were of
that generation - they had no problem doing a rocked form of
jazz.
Miles Davis snuck it in gradually, culminating in
Bitches Brew's full embrace of the idea.
And then Bitches Brew went gold. Here was a way to reach the burgeoning rock/pop audience (where the money was). At first, there was great, adventurous music being made by Miles, early Weather Report, Herbie Hancock's Mwandishi band, and many others. Electric pianos, Fender basses, and straight eighths became commonplace. The original buzz eventually wore off; fusion became a genre, a market unto itself, and began to hobble lucratively towards the LCD.
There was money to be made, but only by downplaying (or eliminating) the jazz content. CBS signed Freddie Hubbard and had him record slick discoid product. Warners signed Stuff, a band of pop session musos, and marketed it (and similar George Benson, Al Jarreau, and David Sanborn, uh... stuff) as "jazz". Hancock did Headhunters, which sounded like bad background muzak from a cop show. Much ridicule from critix, but sales were good.
What is my point? I have none. A moral? Be wary of "jazz" product from major labels, I guess; they (and the musicians involved) perverted the name of jazz to achieve their own financial ends. Now we have the general public thinking Kenny G is a famous jazz musician. We have pop instrumentals being sold under the name of "smooth jazz". Meanwhile, legit fusioneers - like the great French guitarist Nguyen Le - go unnoticed.