There are many different sub-genres within the realm of horror. Slashers are on example, or the more traditional monsters, or torture-porn movies like Saw or Hostel. One common factor is that the fear almost always comes from a malicious force capable of threatening the characters with violence. While looking through the upcoming features at Cornell Cinema, one horror movie caught my eye because it particularly subverts this common feature. Directed by Rodrigo Cortez, the film Buried is a highly unusual. For one, it has a cast of a single actor. The sets? Just one, actually: the entire film is shot inside of a coffin. The entire movie is an observation on one man's struggle to escape from his hopeless situation. See the trailer here: http://www.metacafe.com/watch/5142762/buried_international_movie_trailer/
Obviously, the movie hinges on the character's desperate situation, and there are clear villains that attacked him and buried him alive for ransom money, but these characters are never shown on screen. They don't attack during the movie, and there isn't any visual thrill of violence, there is only the horror of being trapped underground. All the on-screen violence is self-inflicted. It is a very bold idea to make a movie in which the driving violent action, the burial, takes place before the opening scene.
Perhaps because of this lack of obvious violence, the movie isn't even technically considered a horror movie. The IMDB classifies it as Drama, Mystery and Thriller, and Wikipedia calls it a Thriller. However, I have friends that refuse to come watch it with me because they find it too frightening. This makes us question what it is that makes a movie count as Horror. Our first instinct is to say that a horror movie is one which tries to scare us. However, Buried is terrifying to many people but it's merely a thriller because it lacks direct violence. From this we see that it's not fear or discomfort that defines a movie as horror, but instead the term horror is used for any movie which uses fear specifically drawn from the threat of violence, while discomforting movies which don't feature violence are excluded from the genre.
Looking at the relationship between the title Horror and direct violence, it seems limiting that horror movies should, by convention, be limited to being merely aestheticized violent thrills. By virtue of this artificial distinction between movies that are scary, and movies that are scary because of violence, creative movies like Buried are seen as somehow inferior Thrillers, instead of proper Horrors, and are thus discouraged by a genre-aware culture.