By definition, a serial killer is anyone who commits a series of murders with no real motive. So most slasher characters are technically serial killers.
But the term often denotes a certain psychology. It’s a term that is used by detectives and law enforcement. It usually pertains to an “ordinary” person who has a mind unlike most ordinary people. Someone who does not feel remorse, or even somehow enjoys the act of killing.
Cody Meirick on November 4, 2023