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In 2023, hundreds of shootings where multiple people were either injured or killed have been reported in the US. These events are confirmed by local and state law enforcement and covered in media outlets in communities across the country.

Stories about gun violence include terms such as “active shooter,” “mass shooting,” “mass murder,” and “domestic terrorism.” The terms can be easily confused because various organizations and government agencies define them differently.

Being aware of this technicality can help the public more accurately understand the status of a shooting incident, how many people were injured or killed, and, in cases of domestic terrorism, what motivated the incident.

What is an active shooter?

The FBI defines an active shooter as “an individual actively engaged in killing or attempting to kill people in a populated area.” When there is a report of an active shooter, that signals that the incident is currently unfolding and the shooter is not yet apprehended by authorities.

The term describes a person (or people, if there are multiple shooters), but it also describes the status of the situation as “ongoing.”

What is a mass shooting?

The term “mass shooting” can refer to firearm-related events with various outcomes depending on which definition is being used.

A 2020 article from the National Institute of Justice Journal notes the challenges that arise from the lack of a single definition of the term “mass shooting.” Its authors claim that research is “hampered by a lack of agreement on definitions of critical terms, such as ‘mass shootings’ and ‘mass murders,’ and by the absence of consistent sources of data on mass shootings.”

Further, they note that “The federal criminal code lacks a distinct mass shooting offense; this may help explain why researchers use different terminology, or types of criminal offense, in their analyses of the same phenomenon.”

The Department of Justice, for example, shared a 2013 analysis of mass shootings that defines them as “any incident in which at least four people are murdered with a gun.”

News reports on the number of mass shootings in the US are likely to reference the Gun Violence Archive, a nonprofit that defines a mass shooting as an event with a “minimum of four victims shot, either injured or killed, not including any shooter who may also have been killed or injured in the incident.” Many media outlets — such as Reuters, CNN, and the Wall Street Journal — reference this definition of mass shooting. According to that tally, the US has experienced nearly 400 mass shootings so far this year.

What is considered mass murder?

Unlike the terms “active shooter” and “mass shooting,” which specify the use of a firearm, “mass murder,” also called “mass killing,” refers to a number of deaths per event, regardless of the weapon used.

A report from the Congressional Research Service (CRS) cites the FBI in its definition of mass murder: “a multiple homicide incident in which four or more victims are murdered, within one event, and in one or more locations in close geographical proximity.”

However, the same report mentions the ​​Investigative Assistance for Violent Crimes Act of 2012 in which, following the Sandy Hook Elementary School shooting, Congress defined a mass killing as “3 or more killings in a single incident.”

The absence of a collective, agreed-upon definition from the government requires the public to pay close attention to how a story's author or cited sources define these terms.

Are mass shootings considered a form of domestic terrorism?

Not all mass shootings are classified as domestic terrorism — certain elements must be present in the shooter’s intention or motivation, along with “unlawful use or threat of force or violence.”

Specifically, acts of domestic terrorism, which can involve hate crimes, are defined by the FBI as “violent, criminal acts committed by individuals and/or groups to further ideological goals stemming from domestic influences, such as those of a political, religious, social, racial, or environmental nature.”

Incidents that qualify as domestic terrorism and related terminology is further dissected in the FBI’s document: Domestic Terrorism: Definitions, Terminology, and Methodology.

What is considered a gun-related death in the US?

The Centers for Disease Control and Prevention tracks firearm-related deaths — the number of people “dying from a firearm-related injury.” This includes all deaths involving guns, such as homicide, suicide, and accidents.

While there isn’t a single government database dedicated to collecting all firearm-related incidents, there are data on firearm-related deaths in the US collected and collated from public health databases, fatal injury reports, and cause of death reports.

CDC data shows that over the past two decades, firearm deaths in the US have increased by 70% — from their most recent low of 28,663 in 2000, to 48,830 in 2021. More people in the US die from suicide involving a firearm than homicides (including mass killings) or accidents.

Total firearm deaths and their leading causes

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Active Shooter Safety Resources
Advancing Mass Shooting Research To Inform Practice
Analysis of Recent Mass Shootings
Mass Murder with Firearms: Incidents and Victims, 1999-2013