Following up our conversation a couple weeks ago, I present Adam Heine's Official Definition of Speculative Fiction:
1. Speculative Fiction is an umbrella term covering everything that is either science fiction or fantasy.
2. Science Fiction and Fantasy are the two main branches of speculative fiction. Sometimes they overlap.
3. Horror is fiction intended to frighten or scare. It could be sci-fi, fantasy, both, or neither.
4. Magical Realism is not sci-fi, but to quote Terry Pratchett, it's "like a polite way of saying you write fantasy."
5. Everything Else -- paranormal, utopian, dystopian, superhero, apocalyptic, post-apocalyptic, alternate history, urban fantasy, weird fiction, supernatural, and all of the -punks -- is a sub-genre of sci-fi/fantasy.
Among other things, this means there is no speculative fiction that is not either sci-fi or fantasy. You will be very hard-pressed to convince me otherwise.
Here, I made a diagram to help.