In Colfax, La., in 1873; in East St. Louis, Ill., in 1917; and in Tulsa, Okla., in 1921; mobs of white people attacked and killed large numbers of black people. In 1857, a Mormon militia attacked settlers in a wagon train at Mountain Meadows in the Territory of Utah. In 1890, a cavalry regiment gunned down Lakota men, women and children on the Pine Ridge Indian Reservation in South Dakota. In each case, there is disagreement over how many people died, and no certainty about how many were shot, but by most estimates, the death toll was higher than in the Orlando attack.

As a result, some have objected to calling the Orlando mass shooting the worst. The National Association of Black Journalists and the National Association of Hispanic Journalists, for example, issued a joint statement asking reporters to stop using the superlative, “which negates several other incidents in U.S. history, many involving minority victims.”

“You can probably point to some incidents where more people were shot than in Orlando,” said J. Pete Blair, the executive director of the Advanced Law Enforcement Rapid Response Training Center at Texas State University, and an author of an F.B.I. study of active-shooter attacks. “But for our purposes, they’re in a different category. We would consider this to be the worst mass shooting in the United States.”

Disputes over how to define mass shootings are serious enough that experts disagree about whether they are on the rise. Some researchers exclude domestic attacks, but not others. Some say that only the acts of lone gunmen can qualify; others say that a small group of people can carry out a mass shooting if they prepare and act together.