Genre refers to the categorical classification of the work within the scope of its common themes.  Examples include Drama, Horror, Science Fiction, Comedy, Western, Musical, Crime, Adventure, War, Action, Fantasy, Disaster, Thriller, Martial Arts, Teen, and many more. The list continues to grow decade after decade.  For example, the 70's introduced us to the blaxploitation and the disaster genres. The 80's gave us the teen genre. If there is a hot trend it's rewarded with a genre.