According to ye ol’ wikipedia, horror films are movies that seek to elicit a physiological reaction, such as an elevated heartbeat, through the use of fear and shocking one’s audiences.
Inspired by literature from authors like Edgar Allan Poe, Bram Stoker, and Mary Shelley, the horror genre has existed for more than a century. The macabre and the supernatural are frequent themes. Horror may also overlap with the fantasy, supernatural fiction and thriller genres.
Horror films often deal with viewers’ nightmares, fears, revulsions and terror of the unknown. Plots within the horror genre often involve the intrusion of an evil force, event, or personage into the everyday world. Prevalent elements include ghosts, extraterrestrials, vampires, werewolves, demons, satanism, gore, torture, vicious animals, evil witches, monsters, zombies, cannibals, psychopaths, natural or man-made disasters, and serial killers.
Some subgenres of horror include action horror, comedy horror, body horror, disaster horror, holiday horror, horror drama, psychological horror, science fiction horror, slasher horror, supernatural horror, gothic horror, natural horror, zombie horror, first-person horror and teen horror.
Horror Shorts are this but, well, shorter.