I've had this conversation with a friend of mine already. "Spec fic" or "speculative fiction" is a term being used to include "science fiction", "fantasy" and "horror".
Why is anyone using this term? I don't know. It's like using "Violence Fiction" to describe "War", "Spy" and "Detective" genres.
However, it's "specficNZ blogging week", so I thought that I'd contribute.
I think the term "speculative fiction" is lame. I like any of the other terms better. Firstly, if you say you're writing "speculative fiction", people are bound to ask "Are you writing science fiction, horror or fantasy?". It's the kind of term that nose in the air, hoity-toity science fiction writers would use to describe their work. "Oh no, I don't write science fiction, I don't have ray guns and googly eyed little green men, my work is speculative fiction, you know, stuff that could really happen."
This does remind me of the trailer for "Gentlemen Broncos" though. Doctor Ronald Chevalier (played by Jemaine Clement) says, "I'm assuming you love to write fantasy fiction, but the character names in your stories are suffering. Need thou not be afraid. We can add 'onius', 'ainous' or 'anious' to just about anything and it becomes magical."
I can hear Dr. Chevalier using the term "Speculative Fiction" instead of "Fantasy Fiction" and it would fit right in with the poncy tone he uses.