Speculative fiction is a broad genre of fiction with any. Coined by Robert Heinlen, it’s considered an off-shoot of science-fiction, often applied to avoid the limitations of traditional “realistic” sci-fi. In more contemporary times, it’s applied to stories that straddle the line between science-fiction and fantasy.
As a side-note of some amusement, Heinlen insisted it should never be applied to fantasy, but only science-fiction. Of course, Science-fantasy is a sub-genre of speculative fiction that combines elements from both science-fiction and fantasy. The end result is an often messy but usually beautiful tale, broader than either category on its own. Here's the Wikipedia entry. Have fun. Of course, the lack of boundaries is often problematic. Magic must have rules, and science fiction needs the wonder, breadth, and... falls squarely under its umbrella, so that wish has gone unfulfilled.