A horror movie is a movie genre. Horror movies are usually intended to scare the viewer. The main stories of horror movies often involve supernatural forces or characters of evil origin. Horror movies are often confused with thrillers, which are similar.
Slasher movies are a subgenre of horror movies. They are often also a type of thriller movie. Slasher movies normally have a psychopathic killer killing a sequence of people. This is usually in a very violent way.
While movies made as early as 1932 had aspects of slasher movies in them, the genre was not really defined until the late 1970s. The 1974 movie Black Christmas is considered the first slasher movie.[source?]. Halloween (1978) and Friday the 13th (1980) did very well at the box office and showed that slasher movies could make lots of money.