A rifle is a firearm designed to be fired from the shoulder, with a barrel that has a helical groove or pattern of grooves ("rifling") cut into the barrel walls. The raised areas of the rifling are called "lands," which make contact with the projectile (for small arms usage, called a bullet), imparting spin around an axis corresponding to the orientation of the weapon. When the projectile leaves the barrel, the conservation of angular momentum improves accuracy and range, in the same way that a properly thrown American football or rugby ball behaves. The word "rifle" originally referred to the grooving, and a rifle was called a "rifled gun." Rifles are used in warfare, hunting and shooting sports.

Typically, a bullet is propelled by the contained deflagration of an explosive compound (originally black powder, later cordite, and now nitrocellulose), although other means such as compressed air are used in air rifles, which are popular for vermin control, hunting small game, and casual shooting ("plinking").

In most armed forces the term "gun" is incorrect when referring to small arms; in the military, the word "gun" means an artillery piece or crew-served machine gun. Furthermore, in many works of fiction a rifle refers to any weapon that has a stock and is shouldered before firing, even if the weapon is not rifled or does not fire solid projectiles.

Rifles traditionally fired a single projectile with each pull of the trigger. Modern assault rifles are capable of firing in bursts or fully automatic modes, and thus overlap somewhat with machine guns. In fact, many light machine guns (such as the Russian RPK) are adaptations of existing assault rifle designs. Generally, the difference between an automatic rifle and a machine gun comes down to weight and feed system; rifles, with their relatively light components (which overheat quickly) and small magazines, are incapable of sustained automatic fire in the way that machine guns are. While machine guns may require more than one operator, the rifle is an individual weapon.

thumb|350px|Baker rifle File:Rifle Springfield M1903.jpg|thumb|350px|M1903 Springfield

Historical overview

The origins of rifling are difficult to trace, but some of the earliest practical experiments seem to have occurred in Europe during the fifteenth century. Archers had long realized that a twist added to the tail feathers of their arrows gave them greater accuracy. Early muskets produced large quantities of smoke and soot, which had to be cleaned from the action and bore of the musket frequently; either through the action of repeated bore scrubbing, or a deliberate attempt to create "soot grooves" that would allow for more shots to be fired from the firearm might also have led to a perceived increase in accuracy, although no one knows for sure. True rifling dates from the mid-15th century, although the precision required for its effective manufacture kept it out of the hands of infantrymen for another three and a half centuries, when it largely replaced the unrifled musket as the primary infantry weapon. In the transitional nineteenth century, the term "rifled musket" was used to indicate the novel weapon.