1. Any aircraft machine gun of .30 caliber or smaller.

2. In U.S. Army usage, any lightweight machine gun, including the .30-caliber air-cooled machine gun and excluding fully automatic rifles, submachine guns, and machine pistols.

3. In specific nonofficial context, any fully automatic rifle or any machine gun having total weight, with mount, between 20-30 pounds (9-14 kilograms) approximately; for example, the Browning automatic rifle and the Lewis machine gun.