A mass shooting is a violent crime in which one or more attackers use a firearm to kill or injure multiple individuals in rapid succession. Mass shootings with multiple deceased victims are a form of mass murder. There is no widely accepted specific definition of the term, and different organizations tracking such incidents use different criteria. Mass shootings are characterized by the targeting, often indiscriminate, of victims outside a combat setting, and the term generally excludes gang violence, shootouts, and self-defense. The perpetrator of an ongoing mass shooting may be referred to as an active shooter.