Poppet valve:

A device that controls the rate of flow of fluid in a line or opens or shuts off the flow of fluid completely.

When open, the sealing surface of the valve is moved away from a seat; when closed, the sealing surface contacts the seat to shut off flow.

The direction of movement of the valve is usually perpendicular to the seat.

Poppet valves are used extensively as pneumatic (air) controls on drilling rigs and as intake and exhausts valves in most internal-combustion engines.