In general use, an atrocity or massacre designates a politically or ethnically motivated killing of civilians. In international law, more precise terms are war crime and crime against humanity.

An atrocity can be a single specific event or a series of events or can refer to genocide. The defining characteristic of an atrocity is its brutal or systematic nature. It is an act of killing that is in violation of most traditional moral principles, although some societies do not condemn such behavior. Often, hostilities exceed the legitimate mandate of killing enemy combatants to include attacks upon unarmed people, upon combatants after their surrender, or upon otherwise non-combative peoples. Thus, nearly every culture has in its history acts of killing which are atrocities.