Serial murder refers to the unlawful killing of three or more individuals over a period of time, with a cooling-off period between each murder. This pattern distinguishes serial murder from other types of homicide, such as mass murder, where multiple victims are killed in a single event. Typically, serial murderers are driven by psychological gratification, often exhibiting specific motives or signatures in their crimes. Law enforcement agencies study these patterns to understand the behavior of serial killers and to develop strategies for prevention and apprehension.