Genre and Subgenre

Genre is the main category a film falls into, for example thriller. All thriller films have specific components and characteristics to attract a specific target audience.
Subgenre is the use of another less obvious genre to attract an additional target audience, for example romance. Romance is often used as a sub genre to attract more females to watch otherwise male orientated films.

In Time trailer (Thriller/Romance)

Tower Heist trailer (Action/Comedy)