A mass shooting is an incident involving multiple victims of gun violence. There is no widely accepted definition of the term mass shooting. The United States' FBI defines a "mass murder" as "four or more murdered during an event with no "cooling-off period" between the murders." Based on this, it is generally agreed that a mass shooting is whenever four or more people are shot (injured or killed), not including the shooters.
Different media outlets and research groups use different definitions for the term "mass shooting" For example, crime violence research group Gun Violence Archive defines a "mass shooting" as "four or more shot (injured or killed) in a single incident, at the same general time and location, not including the shooter,” differentiating between mass shooting and mass murder and not counting shooters as victims.
The United States’ Congressional Research Service acknowledges that there is not a broadly accepted definition and defines a "public mass shooting" as an event where someone selects four or more people and shoots them with firearms in an indiscriminate manner, echoing the FBI's definition of the term "mass murder", but adding the indiscriminate factor.