26 U.S.C. Sec. 5845 DEFINITIONS OF FIREARM-RELATED TERMS defines the meaning of various terms related to firearms, ammunition, and destructive devices for the purpose of the National Firearms Act. This section defines the following terms: firearm, machine gun, short-barreled rifle, short-barreled shotgun, destructive device, silencer, ammunition, and the term “make” as it relates to firearms and ammunition. It also defines the term “antique firearm” as it relates to the National Firearms Act. The definitions are important for determining the applicability of the Act and its provisions.