The fantasy genre often gets grouped together with - and sometimes confused with - the science fiction genre, but there are some important differences between the two genres. Both fantasy and science fiction are disconnected from reality; they depict worlds that are different from the world we live in. The difference is that the unreal worlds of science fiction stick closer to the world we know; in theory, science fiction doesn't, for example, violate the rules of physics. Fantasy, on the other hand, doesn't give itself any such restrictions; in fantasy, anything goes.
Fantasy allows for the existence of magic, strange creatures, improbable lands and incredible situations. Classic fantasy stories include The Lord of the Rings, with its elves, orcs, hobbits, wizards and dragons. The vampires and werewolves of Twilight fit the fantasy mold, too, as do the superheroes, supervillains and mutants of The Avengers and X-Men.
As these examples make clear, fantasy movies can fall into secondary genres, as well; Twilight is a romance, The Avengers is an action movie, and The Lord of the Rings is an adventure story. The common thread between them is that neither Thor nor Edward Cullen nor Gandalf could exist in the real world as we know it.