An air gun, or airgun, is a gun that shoots projectiles pneumatically with compressed air or other gases that are mechanically pressurized without involving any chemical reactions, in contrast to a firearm, which pressurizes gases chemically via oxidation of combustible propellants that generates propulsive energy by breaking molecular bonds.
Both the "long gun" (air rifle) and "handgun" (air pistol) forms typically propel metallic projectiles that are either diabolo-shaped pellets or spherical shots called BBs, although in recent years Minié ball-shaped cylindro-conoidal projectiles called slugs are gaining more popularity. Certain types of air guns (usually air rifles) may also launch fin-stabilized projectile such as darts (e.g. tranquilizer guns) or arrows (so-called "airbows").
The first air guns were developed as early as the 16th century, and have since been used in hunting, sporting and even warfare. There are three different power sources for modern air guns, depending on the design: spring-piston, pneumatic, or bottled compressed gas (most commonly carbon dioxide).