Since their invention, films (and other things, such as music and subcultures) have been categorised into a number of different genres - groupings based on such characteristics as content, style and presentation. The Internet Movie Database lists 22 such groupings, splitting films accordingly. Entries within a genre can be further whittled down by splitting them into sub-genres, though this can quickly become confusing, as sub-genres also overlap and it is often unclear as to whether a film includes more elements of genre a than it does of genres b and c. What is clear is that in broad terms, genres go through different phases of popularity. At the present time, superheroes are dominating the cinematic landscape, but they are just the latest in a long list of trends that have come and gone and will almost certainly be replaced 'at the top' by something else in time. Even after their fall from mainstream popularity, most genres maintain a core following of fans that ensure at least some form of continued output in cinemas. Some genres, however, like the five featured in this list, have all but vanished from our screens completely, for assorted reasons that will be looked at in due course.