Schrader valve
A schrader valve, often called a "tire valve", "tank valve" or "sniffler valve" because schrader is a brand name, is used in hybrid and pneumatic launchers to allow you to fill them with air. They are also used, less frequently, in combustion launchers, to allow you to vent them.
They accept the standard air chuck used to fill tires, allowing you to fill them with a standard bicycle pump. Alternative valves exist, most notably the quick disconnect which is more expensive, but has a higher amount of flow.