The M134 Minigun is a 7.62x51 mm NATO, six-barreled machine gun with a high rate of fire (2,000 to 6,000 rounds per minute).
It features Gatling-style rotating barrels with an external power source, normally an electric motor. The "Mini" in the name is in comparison to designs that use a similar firing mechanism but larger shells, such as General Electric's earlier 20-millimeter M61 Vulcan, and "gun" for a caliber size smaller than that of a cannon, typically 20 mm and higher.
The Minigun is used several branches of the U.S. military. Versions are designated M134 and XM196 by the United States Army, and GAU-2/A and GAU-17/A by the U.S. Air Force and U.S. Navy.
"Minigun" refers to a specific model of weapon that General Electric originally produced, but the term "minigun" has popularly come to refer to any externally powered Gatling gun of rifle caliber. The term is also used to refer to guns of similar rates of fire and configuration regardless of power source and caliber.