n A device that controls the flow of a gas or fluid through a pipe.
n A device that admits fuel and air into the cylinder of an internal combustion engine, or one that allows combustion gases to exit.
n (anatomy) One or more membranous partitions, flaps, or folds, which permit the passage of the contents of a vessel or cavity in one direction, but stop or retard the flow in the opposite direction; as, the ileocolic, mitral, and semilunar valves.