A monster is a type of fictional creature found in horror, fantasy, science fiction, folklore, mythology and religion. Monsters are very often depicted as dangerous and aggressive, with a strange or grotesque appearance that causes terror and fear, often in humans. Monsters usually resemble bizarre, deformed, otherworldly and/or mutated animals or entirely unique creatures of varying sizes, but may also take a human form, such as mutants, ghosts, spirits, zombies, or cannibals, among other things. They may or may not have supernatural powers, but are usually capable of killing or causing some form of destruction, threatening the social or moral order of the human world in the process.

Horror is a genre of fiction that is intended to disturb, frighten or scare. Horror is often divided into the sub-genres of psychological horror and supernatural horror, which are in the realm of speculative fiction. Literary historian J. A. Cuddon, in 1984, defined the horror story as "a piece of fiction in prose of variable length... which shocks, or even frightens the reader, or perhaps induces a feeling of repulsion or loathing". Horror intends to create an eerie and frightening atmosphere for the reader. Often the central menace of a work of horror fiction can be interpreted as a metaphor for larger fears of a society.