A maneuver used in professional wrestling. The executor sets it up by placing his opponent in a standing fireman's carry. He then proceeds to drop the user sideways so that his head crashes into the canvas. (Although taller wrestlers performing the maneuver often will flip the person over completely.)
The move was popularized in the US in the mid-90s by Louie Spicolli in ECW, although it likely was already being used in Japan.
"It almost looked like the Brooklyn Brawler had the match won, but Tommy Dreamer hit him with the Death Valley Driver, knocking him out cold."