Most genres have elements that the audience expects as they have been used many times in previous films from their genre/sub genre. The conventions of a film in the horror genre are: -Either a dark isolated setting e.g. forest/abounded building.
Thriller is a genre of literature, film, videogame stories and television programming that uses suspense, tension, and excitement as its main elements. Thrillers heavily stimulate the viewer's moods, giving them a high level of anticipation, ultra-heightened expectation, uncertainty, surprise, anxiety and terror.
Horror is a film genre seeking to elicit a negative emotional reaction from viewers by playing on the audience's primal fears. 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, commonly of supernatural origin, into the everyday world. Prevalent elements include ghosts, extraterrestrials, vampires, werewolves, demons, gore, torture, vicious animals, evil witches, monsters, zombies, cannibals, and serial killers. Movies about the supernatural are not necessarily horrific.
Romance film can be defined as a genre wherein the plot revolves around the love between two protagonists. This genre usually has a theme that explores an issue within love, including but not limited to: love at first sight, forbidden love, love triangles, and sacrificial love. The tone of Romance film can vary greatly. Whether the end is happy or tragic, Romance film aims to evoke strong emotions in the audience.