The essential definition of a cult movie is: a controversial film that has acquired a passionate fanbase. Let’s add that a cult movie has followers that engage in repeated viewings, that quote dialogue, and write and talk actively about the movie. On the other hand, there’s a strong opinion mentioning a cult movie should be a non-mainstream, non-Hollywood one.
So, what we do with movies as Star Wars (1977), Casablanca (1942), Terminator (1984) and more recently The Fast and the Furious (2001)? These are blockbusters and comply with the cult film definition.
Moreover, a cult movie should have a distinct narrative or aesthetic. But as in other aspects of art this is not always evident. So the ground is that a movie is a cult movie when someone says it is. Let’s retake the joke about pornography: how you differentiate between artistic nudity and pornography? Easy, when you see it. However, a cult movie still needs followers to talk about it and a fanbase, still one fan is a fanbase.
Some say a cult movie should have a subversive or controversial message. I think subversion is not be a not a sine qua non condition, but the controversial element must exist in a cult movie. A good example is the Blair Witch Project (1999), controversial? yes, subversive? not that I can see it.
There are also cult movie directors, such as Stanley Kubrick, Luis Buñuel, and Quentin Tarantino and here we face again the conflict of commercial movie vs. cult movie. for instance, George Lucas, a Hollywood blockbuster specialist, who’s first two movies were cult films: American Graffiti (1973) and Star Wars (1977). Another example of cult movie, blockbuster director is Steven Spielberg, watch Jaws (1975) and E.T. (1982).
Finally, outside the USA is a whole world of cult movies. Das Cabinet des Dr. Caligari (1920) (The Cabinet of Dr. Cagliari) by Robert Wiene, is the first cult movie ever made. While Nosferatu: Phantom der Nacht by Werner Herzog (1979) was the first remake of a cult movie, of Nosferatu, eine Symphonie des Grauens (1922) by F. W. Murnau, that also became a cult film.
Cult movie directors mushroom outside the US, one of my favorites is Italian Dario Argento, whose movies are a commercial failure and not cult movies in the US, whereas in the rest of the world Argento’s films are immediately cult movies. Moreover, there are also cult movie actors in the non-US cinema, Mexican actor Mario Moreno “Cantinflas” is both a cult movie and blockbuster star. Just because he performs in a movie, the movie is a cult film, e.g.: Ahí está el detalle (1940), which is not even included in the IMDb website, but still 80-years later Cantinflas subversive performance on it is admired and quoted, his way of dressing imitated, and the title of the movie itself has achieved status of a popular byword in Spanish-speaking countries.