In a car that is equipped with some sort of forced induction system ,such as a turbo or a supercharger, a blow-off valve is usually availible as an aftermarket part to release excess pressure (boost) from the turbine system. Makes a very distinct noise. Like - pssssshhhhhhhhh! Or somtimes a chirping noise depending on the blow-off valve. Usually replaces a stock part usually refered to as a by-pass valve.
1. Gil: Whoah, dude! Did you hear that car go by?
Willy: Yeah, it sounded like it had a blow-off valve.
Creators of the hit PC title Half-Life, and its subsequent expansion-packs. Also recently implemented the Steam network, a method of software delivery intended to eliminate the middle-man ie. chains like Electronic Boutique and GameStop. Also currently working on Half-Life 2.
"Man, Half-Life 2 is gonna be delayed forever."
"Yeah, but it'll probably be worth the wait."