Assault rifle

By U.S. army definition, a selective-fire rifle chambered for a cartridge of intermediate power.

Assault weapon

Any weapon used in an assault. Usually refers to selective-fire firearms that are capable of fully automatic, semiautomatic, or burst fire.

Automatic

A firearm designed to feed cartridges, fire them, eject their empty cases and repeat this cycle as long as the trigger is depressed and cartridges remain in the feed system. Examples: machine guns, sub-machine guns, selective-fire rifles, including true assault rifles.

Background check

An investigation of a gun purchaser's background through the state police or the FBI to determine if the purchaser is prohibited from buying a gun.

Ballistic fingerprint

The unique marking a gun leaves on a bullet after a bullet has been fired from the gun.

Brady Law

A federal law that requires federally licensed dealers to perform background checks on gun purchasers.

Child Access Protection (CAP) laws

Laws that require adults either to store loaded guns in a place where children reasonably cannot get to them or to use a device to lock the gun so children cannot access them.

Firearm

A rifle, shotgun or handgun using gunpowder as a propellant.

Gunpowder

Chemical substances of various compositions, particle sizes, shapes and colors that, on ignition, serve as a propellant.

Handgun

Synonym for pistol.

Pistol

Synonymous with "handgun." A gun that is generally held in one hand. It may be of the single-shot, multi-barrel, repeating or semi-automatic variety and includes revolvers.

Rifle

A shoulder gun with rifled bore.

Semi-automatic

A firearm designed to fire a single cartridge, eject the empty case and reload the chamber each time the trigger is pulled.

Sub-machine gun

An automatic firearm commonly firing pistol ammunition intended for close-range combat.

Source:
Dictionary.com [1]
Airboat Association of Florida [2]