Genre refers to a system of signs and themes that define a particular style of film, such as westerns featuring cowboys, horses, guns, and battles with Native Americans. Genres act as a contract between audiences and filmmakers, allowing audiences to build expectations about what will happen based on generic conventions. While genre boundaries can be flexible, with some films combining elements of different styles, common film genres include horror, thriller, comedy, romantic comedy, action, science fiction, western, musical, and war.