What is Firearm?

Legal Definition
A firearm is a portable gun - a barreled weapon that launches one or more projectiles, often driven by the action of an explosive force. The first primitive firearms originated in 13th-century China when the one-person-portable fire lance was combined with projectiles. The technology gradually spread through the rest of East Asia, South Asia, the Middle East and then into Europe. Older firearms typically used black powder as a propellant, but modern firearms use smokeless powder or other propellants. Most modern firearms (with the notable exception of smoothbore shotguns) have rifled barrels to impart spin to the projectile for improved flight stability.

Modern firearms can be described by their caliber (i.e. their bore diameter; this is given in millimeters or inches e.g. 7.5mm, .357) or in the case of shotguns their gauge (e.g. 12 ga.); by the type of action employed (muzzle, breech, lever, bolt, pump, revolver, semi-automatic, automatic etc.) together with the usual means of deportment (hand-held or mechanical mounting). Further classification may make reference to the type of barrel used (rifled) and to the barrel length (19 inch), to the firing mechanism (e.g. matchlock, wheellock, flintlock, percussion lock), to the design's primary intended use (e.g. hunting rifle), or to the commonly accepted name for a particular variation (e.g. Gatling gun). The word firearms usually is used in a sense restricted to small arms (weapons that can be carried by a single person), whereas the word artillery covers larger gunpowder-fired weapons.

Shooters aim firearms at their targets with hand-eye co-ordination, using either iron sights or optical sights. The accurate range of pistols generally does not exceed 100 yards (91 m), while most rifles are accurate to 550 yards (500 m) using iron sights, or to longer ranges using optical sights (firearm rounds may be dangerous or lethal well beyond their accurate range; the minimum distance for safety is much greater than specified range). Some purpose-built sniper rifles are accurate to ranges of more than 2,200 yards (2,000 m).
-- Wikipedia
Legal Definition
This word comprises nil sorts of guns, fowling-pieces, blunderbusses, pistols, etc. Harris v. Cameron, 81 Wis. 239, 51 N. W. 437, 29 Am. St. Rep. 891; Atwood v. State, 53 Ala. 509; Whitney Arms Co., v. Barlow, 38 N. Y. Super. Ct. 563.
-- Black's Law Dictionary
Legal Definition
This term is used to describe a weapon that acts from a gunpowder explosion.