A device found in cars to prevent the car from moving by blocking the wheels.
It is usually operated by a lever to the right-hand side (left for britain, and most former british colonies) of the driver (between the passenger's seat and the driver's seat).
It is used when parking the car (so it won't roll onto the road, or down a hill) or when making a handbrake turn.
It also appears to be slang
for something, but I don't know what...