The civilian version of military guns, defined in federal law as semi-automatic firearms with a detachable magazine and certain features such as a folding stock, bayonet mount, or pistol grip (allowing an assault rifle to be fired with one hand). The manufacture of new assault weapons was banned in 1994, but weapons made before the ban continue to be easily and legally available, except in states that have legislated to prohibit such sales. One of the guns used in the Columbine massacre was a pre-ban TEC-DC9 assault pistol, purchased by the killers at a gun show.
 

A check of official records to determine whether an individual who wants to buy a gun falls into any of the "prohibited" categories, such as convicted felons, fugitives from justice, and people subject to restraining orders for domestic violence. The federal Brady law requires gun dealers to contact the FBI's National Instant Background Check System (NICS) before selling someone a gun. If NICS reveals that the customer is a prohibited purchaser, the dealer must refuse to make the sale. Some states also require dealers to check state criminal records, which contain more information than NICS alone. The Brady law only applies to sales by licensed firearm dealers (FFLs). Thus, in most second-hand gun sales, no background check is required by law. This gap means that around 40% of all handgun sales—between individuals, at garage sales, flea markets and gun shows—are not subject to background checks. To close this loophole, several states have passed their own laws requiring background checks in all gun sales, or in all handgun sales.
 

A licensed dealer is someone who holds a license to sell guns. To qualify as an FFL, an applicant undergoes a background check, submits a photograph and fingerprints, and pays a fee of $200 for three years. The law imposes obligations on FFLs that do not apply to other people selling guns: to run background checks on buyers, report the theft of guns, and assist with gun-tracing requests from the Bureau of Alcohol, Tobacco & Firearms. In return, FFLs are allowed to receive and transport unlimited quantities of guns across state lines, an activity that is otherwise prohibited by federal law. There are around 100,000 FFLs, although fewer than 15% actually operate gun shops. The majority operate from their homes.  Compare Private seller.
 

A gun show is a temporary market for guns and ammunition, usually held at a meeting hall or fairground. Over 4400 gun shows were advertised around the country in 1998; on average 2500—5000 people attend per show. Anyone can sell guns at these shows: generally at least 25% of the sellers are not licensed dealers. Since these sellers are not required to run Brady background checks on buyers, gun shows are an important source of guns for criminals who would not be able to buy weapons in a store. The absence of background checks by these sellers is known as the gun show loophole. In the November 2000 elections, voters in Colorado and Oregon approved historic state ballot initiatives to close the gun show loophole.   more
 

A gun designed to be fired from one hand, capable of being concealed on the person and with a barrel less than 16 inches long. Until the mid-1980s the most common type was a revolver, with a rotating cylinder usually holding 6 cartridges. Since then, production of revolvers has declined and the dominant handgun has become the semi-automatic pistol, which uses a removable ammunition magazine (also called a "clip"), usually located in the handle of the gun. Each firing of the pistol forces a new cartridge up the magazine and into the chamber. A typical 9mm-caliber pistol has a magazine capacity of 8-10 cartridges.
 

An official certificate confirming that an individual has met the legal requirements to own or use guns. Under federal law, any adult is allowed to have guns unless they are disqualified by their criminal record. Under a licensing system, the only people allowed to have guns are those who have taken active steps to qualify. Several states have passed laws requiring a license as a prerequisite for gun ownership. The criteria vary in these states, but licensing usually requires proof of training or knowledge of gun safety.
 

Federal law prohibits possession of a handgun by anyone under 18, but some states have established higher or lower age limits. For example, Montana has set the minimum age for handgun possession at 14. There is no federal minimum age for possession of a long gun (rifle or shotgun). Licensed dealers (FFLs) are prohibited from selling handguns to people under 21, and long guns to people under 18. Unlicensed sellers may not sell handguns to people under 18, but there is no federal minimum age for buyers of rifles or shotguns. Some states have set their own age limits.
 

Someone who is not a licensed dealer, and who therefore is not subject to the basic requirements of the federal gun law. Private sellers do not have to run background checks on buyers, report the theft of guns, or assist with gun-tracing requests. Their only obligation under federal law is not to provide handguns to people aged under 18. Around 40% of all handgun transactions involve these non-licensed sellers. To regulate these transactions, some states have passed laws requiring background checks by all gun sales.  Compare Licensed dealer.
 

An official record of the transfer of a gun from one owner to another. This makes the owner accountable for the gun. Registration serves three crucial purposes in preventing gun violence:
 

	When legal gun owners decide to sell or give away their guns, registration requires them to ensure that they do so in accordance with the law.
	If someone who already owns a gun is convicted of a felony, registration notifies the police that the gun is now illegally possessed.
	When police are sent to investigate a disturbance, registration tells them whether they are likely to encounter a gun at that address.

Registration also assists the police after a crime is committed. If the crime gun is recovered, police can determine the last legal owner. In future, as more states use ballistic fingerprinting, registration will help to trace the last legal owner even if the gun itself is not recovered. See also Straw Purchase.
 

State law requiring firearms to be stored with a trigger lock, cable lock, or in a locked container so that they cannot be fired. Only Massachusetts requires that all firearms be secured through the use of a locking device or safe. Three other states—California, Connecticut, and Hawaii—have this requirement for handgun owners only.
 

A requirement that purchasers pass a safety test before they can possess a gun. For example, in Hawaii, prospective purchasers must sit for a written test covering gun safety and firearm laws, followed by hands-on instruction at a firing range. Four states require some form of safety testing as a prerequisite for owning a gun.
 

A low-quality semi-automatic pistol, short-barreled (usually less than three inches) and easily concealed. Because they are small and inexpensive, Saturday Night Specials are especially popular with juvenile criminals. Federal law bans their importation into the US, but allows domestic production and sales of these same weapons. To close this loophole, seven states have passed their own laws banning commercial sale of junk guns.
 

When the buyer of a gun is acting on behalf of a prohibited purchaser, such as a convicted felon, a juvenile, or a domestic violence offender. The straw purchaser passes the background check, buys the gun, and gives or sells it to the prohibited person. This allows someone who would have not passed the background check to circumvent the law and obtain a firearm. Straw purchases are an important avenue for guns to move from the legal to the illegal market. Once a gun leaves the dealer's premises, federal law does not require any record of subsequent sales. To close this loophole, some states have implemented firearm registration, which holds the first purchaser accountable for the gun. See also Registration.
 

The illegal movement of weapons from one locality to another, exploiting the lack of uniformity in gun laws. Traffickers buy firearms legally in places where gun sales are not regulated, then transport and sell them illegally in places with more restrictive laws. Florida, Georgia, Mississippi and Texas are the major source states for trafficked guns: in 1999, one in four guns used in out-of-state crimes was trafficked from those states. Trafficking can also occur within one state. For example, most handguns used in crime in Chicago are trafficked from surrounding counties where the local gun laws are much weaker.
 

A device that can be secured to a gun to prevent the trigger being pulled. Since trigger locks are not built into the gun itself, their effectiveness depends on the owner remembering and making the effort to secure the lock after each use. In late 1997, the major handgun manufacturers agreed to supply trigger locks with all new handguns. This was a voluntary agreement and compliance has been inconsistent. Five states have passed laws requiring that trigger locks be provided with all new handguns sold.
 

A mandatory "cooling off period" before a buyer actually takes possession of the gun, which also permits a more thorough background check. Until November 1998 the Brady law required a five-day waiting period for all handgun purchases from federally licensed dealers (FFLs). Since that requirement was abolished, there is now no minimum waiting period under federal law. However, some states have passed their own laws.