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Mass shooting

A mass shooting is a violent incident in which one or more people use firearms to kill or injure multiple victims in a single event.

By Ethan Anderson| Reviewed by Olivia Bennett, Standards & Fact-Checking Lead| Updated July 27, 2026|2 min read| Fact-checked

A mass shooting is a violent incident in which one or more people use firearms to kill or injure multiple victims in a single event. There is no single universally accepted legal or research definition; thresholds commonly range from four or more people shot to four or more people killed, depending on the source.

Definition

Mass shooting is a broad term for an incident in which firearms are used to shoot multiple people in a single event. Sources disagree on the minimum number of victims and whether injuries, fatalities, or both are counted.

Competing definitions

Research organizations, media outlets, and government-related sources use different thresholds. Common approaches include four or more people shot, four or more people killed, or other event-based criteria.

Use in crime data

Because the term lacks a standard definition, comparisons across studies and databases can produce different counts of mass shootings. This makes trends, totals, and policy analysis difficult to compare directly.

Relationship to mass murder

When a mass shooting results in multiple deaths, it may also be classified as mass murder. Some sources treat mass shootings as a subset of mass murder, while others keep the terms separate.

Key facts

  • There is no single official or universally accepted definition of a mass shooting.
  • Some sources define it as four or more people shot, whether injured or killed.
  • Other sources use a fatality-based definition, such as four or more people killed.
  • The FBI is widely described as defining 'active shooter' incidents, but not as setting a single standard mass-shooting threshold.
  • Definitions often exclude gang violence, terrorism, and warfare, depending on the dataset or researcher.
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Canadian context

Canadian readers may encounter the term in news reporting, academic research, and cross-border comparisons of gun violence, especially because definitions vary between Canadian, U.S., and international sources.

Frequently asked questions

What is a mass shooting?
It is a violent incident in which one or more people use firearms to shoot multiple victims in a single event.
Is there an official definition?
No single universally accepted definition exists. Different sources use different thresholds and criteria.
How many victims are usually involved?
A common threshold is four or more people shot, but some definitions instead focus on four or more people killed.
Does the definition include injuries as well as deaths?
Often yes, but not always. Some databases count anyone shot, whether injured or killed, while others count only fatalities.
Are gang shootings or terrorism included?
Sometimes not. Many definitions exclude gang violence, terrorism, and warfare, but this depends on the source.
Is mass shooting the same as mass murder?
Not exactly. A mass shooting can overlap with mass murder when multiple people are killed, but the terms are not always used interchangeably.

References

  1. Wikipedia — https://en.wikipedia.org/wiki/Mass_shooting
    Supports: General overview and example of the broad, contested usage of the term.
  2. Encyclopaedia Britannica — https://www.britannica.com/topic/mass-shooting
    Supports: Notes that definitions vary and discusses FBI-related usage and mass killing distinctions.
  3. RAND Corporation — https://www.rand.org/research/gun-policy/analysis/essays/mass-shootings.html
    Supports: Explains that there is no standard definition and summarizes common research thresholds.
  4. Gun Violence Archive — https://www.gunviolencearchive.org/explainer/mass-shooting-methodology-and-reasoning
    Supports: Defines mass shooting as four or more victims shot, excluding the shooter.
  5. Everytown Research — https://www.everytownresearch.org/wp-content/uploads/sites/4/2023/03/Mass-Shooting-Report-Methodology.pdf
    Supports: Uses a definition based on four or more people killed or injured with a firearm, excluding the perpetrator.
  6. Congressional Research Service — https://www.congress.gov/crs_external_products/R/PDF/R48276/R48276.2.pdf
    Supports: Summarizes federal and research definitions and the lack of a single consensus standard.