Piston

PISTON-
A piston is a component of reciprocating engines,
reciprocating pumps, gas compressors and pneumatic
cylinders, among other similar mechanisms. It is the moving
component that is contained by a cylinder and is made gas-
tight by piston rings. In an engine, its purpose is to transfer
force from expanding gas in the cylinder to the crankshaft
via a piston rod and/or connecting rod. In a pump, the
function is reversed and force is transferred from the
crankshaft to the piston for the purpose of compressing or
ejecting the fluid in the cylinder. In some engines, the piston
also acts as a valve by covering and uncovering ports in the
cylinder wall.