Semi-automatic gun:  A gun that fires rapidly but only with each separate pull of the trigger (whereas an automatic fires repeatedly, so long as the trigger is pulled).  Most guns made today are semi automatics, other than revolvers and bolt-action hunting rifles.

Bump stock: a plastic device attached to an assault rifle that uses the recoil (bump back) of the rifle to fire rapidly, mirroring the firing of an automatic.

FFL (Federal Firearms License): Anyone engaged in the business of selling or making firearms is required to have an FFL and follow FFL regulations, such as conducting a background check of buyers.  This would apply to gun shops and pawn shops.   But someone not fully engaged in selling guns (e.g., on a part time basis), referred to as a “private seller,” is not required to have an FFL or conduct a background check.

Magazines:  an ammunition storage device that feeds bullets into a repeating firearm.  They are usually removable (detachable), allowing the user to remove it once empty and attach another.  They come in many capacities, from 7 rounds to 10, 15, 30, 50 and even 100.

School resource officers:   law enforcement officers responsible for providing security and crime prevention services in schools

NICS (National Instant Criminal background check System): national database system operated by the FBI that checks available records of persons seeking to purchase a gun to determine if they are disqualified from receiving firearms.  The systems relies on states, the military, courts and law enforcement to submit criminal records and other disqualifying data.

CCW:  Carrying a Concealed Weapon or Concealed Carry Weapon; this refers to the practice of carrying a weapon (normally a handgun) in public in a concealed manner, either on one’s person or in close proximity (as opposed to “open carry,” in which someone can see your weapon.)