A Gun is a weapon which fires a bullet, dart or other projectile.
The three main types of modern firearms today are bolt-operated, semi-automatic, and automatic weapons. In a bolt-action weapon, each new round must be chambered manually, by moving the breech to eject the empty casing. In semi-automatic weapons, each pull of the trigger fires a bullet. In fully automatic weapons, bullets will be fired as long as the trigger is depressed until either the trigger is released, or the ammunition is exhausted.
Science fiction, such as Star Trek, has postulated many different types of directed energy weapons. These are guns that fire beams, waves, or packets of energy. Some energy guns can be set to stun, not to wound or kill.
The cultural issues surrounding guns are many and widely debated. Conservatives generally prefer to reserve for the individual the right to self-defense through the use of guns and other weapons. Liberals generally prefer to delegate this right to guards, police, and the military.[Citation Needed]
Law-abiding citizens carrying guns are statistically an effective deterrent and defense against lawless or criminal individuals. This has certainly been shown in the USA, which had 11,350 murders by shooting in 2005, compared with 50 in 2005/06 in the UK, which restricts the possession of handguns. However, it should be noted, that the USA has a population approximately 5 times greater than the UK,  the number of murders by shooting is approximately 200 times higher.
Guns are also a defense against a tyrannical government. Theoretically, if a person has the power to take the life of another, other people will not perpetrate criminal offenses against them. In practice, few existing civilian militias are strong enough to withstand sustained warfare by a government's army. Also, countries with high rates of gun ownership, such as present-day Iraq or many countries in sub-Sharana Africa, are not guaranteed to have a low crime rate.
In the military, the word "gun" is usually used to describe a weapon with an area effect. Examples include some indirect fire weapons such as field guns, large-caliber cannons (greater than 20mm), and machine guns.[Citation Needed]