The agreed-upon definition of active shooter by US government agencies (including the White House, US Department of Justice, FBI, US Department of Education, US Department of Homeland Security, and Federal Emergency Management Agency) is “an individual actively engaged in killing or attempting to kill people in a confined and populated area.”
Active shooter or active killer describes the perpetrator of a type of mass murder marked by rapidity, scale, randomness, and often suicide. The United States Department of Homeland Security defines an active shooter as “an individual actively engaged in killing or attempting to kill people in a confined and populated area; in most cases, active shooters use firearms and there is no pattern or method to their selection of victims.”