A type of motorcycle crash wherein the rider is catapulted over the motorcycle as a result of the rear wheel losing traction, sliding out to one side, and then abruptly regaining traction while still out-of-line with the front wheel. Much more dangerous than a lowside.
Can be used as a noun or a verb:
Verb: "He was leading the race until he highsided coming out of the eighth turn."
Noun: "I've wrecked many times, but nothing is more terrifying than a highside."