There have been 273 mass shootings in the United States since Jan. 1, 2017.
Another one happened in Las Vegas on Sunday. The shooting there is believed to be the deadliest single-day mass shooting in U.S. History.
While there is not a specific definition of a mass shooting, an accepted one says that an incident in which at least four people are shot (injured or killed) is considered a “mass shooting.”
The FBI uses a similar definition for a “mass murder,” only the Bureau considers an incident a mass murder if three or more people are killed.
Federal statutes define "mass killing" as three or more people killed, regardless of weapons.
Mass Shooting Tracker, a website that tracks shooting incidents across the country, defines a mass shooting as any incident in which four or more people are shot, whether injured or killed.
By anyone’s definition, a mass shooting can be carried out by an individual or by a group.