"Airsoft guns are replica firearms, or a special type of air guns used in airsoft, that fire spherical projectiles of many different materials, including (but not limited to) plastic, aluminum, and biodegradable material. This is achieved by a technical solution of either:
compressed gas
spring-driven piston
electrical piston
a combination of electrical- and spring-driven piston
hydraulics
Depending on the mechanism for driving the pellet, an airsoft gun can be operated manually or on a cyclic basis. The cycling mechanism is implemented by either compressed gas (such as Green Gas [mix of propane and silicone] or CO2) or by compressed air (via a spring or an electric motor pulling a piston).
The Airsoft guns are designed to be non-lethal and to provide realistic replicas."