There's no question that there's overlap and this question is tough. From one perspective all fiction is fantasy since it begins with a set of assumptions that are most likely of appeal to the author.
I've recently been trying to make lists of "fantasy movies" or "fantasy books" with the aim of writing online reviews. I keep finding myself hitting a brick wall when it comes to a clear definition.
Here's my attempt:
Fantasy focuses more on magic and imagination than technology and rational explanation (fantasy is not science fiction) Fantasy focuses more on heroes and struggles rather than dread and overwhelming fear (fantasy is different than horror) Pure fantasy is not about any element in the story but about the attitude of the story -- such as wonder, beauty, supernatural forces, and especially a heroic journey. What do people think? Is there an agreed upon definition of fantasy? How do we determine when a movie or book is fantasy as opposed to horror or science fiction?