Mass shootings are incidents involving several victims of firearm-related violence.
The precise inclusion criteria are disputed, and there is no broadly accepted definition.
[1][2] The Gun Violence Archive, a nonprofit research group that tracks shootings and their characteristics in the United States, defines a mass shooting as an incident in which four or more people, excluding the perpetrator(s), are shot in one location at roughly the same time.
[4][5] The crowdsourced Mass Shooting Tracker project uses a definition even looser than the Gun Violence Archive's definition: four people shot in one incident regardless of the circumstances.
[6] Larger documentation of mass shootings in the United States has occurred through independent and scholarly studies such as the Stanford University Mass Shootings in America Data Project.