While a serial killer murders in separate instances, a mass murderer kills many people in a single event. According to Science Direct, the term "mass murder" was first used in a 1982 New York Times article. Unlike a serial killer, a mass murderer doesn't have a cool-off period and takes the lives of at least four individuals in one incident. Those who commit familicide — in which the perpetrator takes the lives of several family members — also fall under the category of a mass murderer.
Mass murders can be carried out by individuals, organizations, or even the government. An example of a mass murderer is James Oliver Huberty, a mentally unstable man who randomly opened fire at a McDonald's restaurant in California, in 1984. He killed 21 people and left many others wounded within an hour of the attack, per History. On a large scale, genocide is one example of mass murder, such as what happened during the Holocaust when the Nazis killed millions of Jews.
