What is a horror movie?

The personal convention of a horror movie:
Horror movies tell a story while, through out the film, try to achieve one objective. This objective is to scare the audience. Horror movies attempt to provoke emotions of fear, horror and terror from the viewers. The plot usually involves themes of death, the supernatural or mental illness.
The audience usually receives a vicarious thrill through witnessing a story that deals with the fears of the audience as it places us in situations we would not usually experience, or wish to experience. The audience holds no control over the situation and as the conclusion of a characters life draws near the audience begins to receive an adrenalin kick which is what the audience wishes to see.

The ideological conventions of a horror movie:
The implicit (hidden) or explicit (obvious) messages are rooted inside the narrative, as to provide ideologies so that the audience is made to believe that the people who abide to the rules are the ones who survive. There are themes of punishment, rejection and/or revulsion at subject which move away from ‘correct’ thinking for example the girl who indulges in alcohol and sex is probably the one who will die early on however the innocent girl who does none of these things will not die at all. Horror movies tend to up hold dominate ideologies by taking people who are not like us, e.g. patients from a mental hospital, and making them the killer within a movie because they are not like us and thereby different and should be feared.