Horror is a genre of storytelling which plays on the audience's emotions, particularly the sense of fear. Horror fiction is deeply-rooted in the world's cultures, probably going back to stories told by early humans as the shadows lengthened around their fires. Much horror literature also elicits emotions such as disgust and outright terror. Two of the most famous characters of Western horror are Frankenstein's monster and Dracula, which both involve the familiar human form presented in a terrifying way.
Horror stories generally involve a semi-familiar setting, with certain key properties subverted, alongside some form of danger which often involves physical or psychological unpleasantness, with death a constant risk. For example, Bram Stoker's famous vampire is in many ways a gentleman and an aristocrat, familiar with the social niceties of his day, but in reality is a blood-sucking fiend compelled to drain the innocent. Likewise, the ghosts of tales such as those of M.R. James are in some ways recognisably human, motivated by such emotions as revenge or anger, but are also identifiable by their special supernatural properties.
Whereas in other genres, in which the reader or viewer is safely able to enjoy the story, horror invokes a sense of unease, drawing them in and making them share the feelings of the characters whose lives gradually spiral out of their control. Horror films particularly emphasise this, making full use of camera techniques and special effects to terrify the viewer. This plus the ability of horror to mix with other genres such as comedy (Scream) or even science fiction (Alien), makes the genre highly flexible, adapting to the fears of the day.