...and ever since generations of electric guitarists have been confused over tremolo and vibrato, because Leo Fender mixed them up.

One the the Stratocaster's major innovations was a bridge system that allowed for large string bends without messing up intonation. For unknown reasons he called this a tremolo system, even though the effect produced using it is vibrato (varying pitch) rather than tremolo (varying volume).

He did a similar thing with the Fender Vibrolux amp. That had a tremolo effect built in, but Fender marketed as vibrato.