The act of fuckin a loose hoe, whose pussy is so loose a man's crank will slap around in it.
When I was fuckin Cathy i suffered from piston slap.
by Paul Trahan April 21, 2003
1 more definition
In a internal combustion engine when the cylinder is oversized and the piston will rock side to side producing a knocking sound.
Chad's car has really bad pistion slap
by Nobis July 29, 2003