Airsoft guns are replica toy guns used in airsoft sports. They are a special type of low-power smooth bore air guns designed to shoot non-metallic spherical projectiles often colloquially (but incorrectly) referred to as "6mm BBs", which are typically made of (but not limited to) plastic or biodegradable resin materials.
Depending on the design mechanism for pellet propulsion, airsoft guns can be categorized into two groups: mechanical, which consists of a coil spring-loaded piston air pump that is either manually cocked (e.g. spring guns) or automatically cycled by a battery-powered electric motor gearbox (e.g. AEGs); and pneumatic, which operates by valve-controlled release of pre-filled bottled gas such as compressed propane mixed with silicone oil (commonly known as "Green Gas") or CO2 canisters (e.g. GBB guns).