Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Speculative fiction is a fiction genre speculating about worlds that are unlike the real world in various important ways. In these contexts, it generally overlaps one or more of the following: science fiction, fantasy fiction, horror fiction, supernatural fiction, superhero fiction, utopian and dystopian fiction, apocalyptic and post-apocalyptic fiction, and alternate history.The term is often attributed to Robert A. Heinlein. In his first known use of the term, in editorial material at the front of the 2/8/1947 issue of The Saturday Evening Post, Heinlein used it specifically as a synonym for "science fiction"; in a later piece, he explicitly stated that his use of the term did not include fantasy. Heinlein may have come up with the term himself, but there are earlier citations: a piece in Lippincott''s Monthly Magazine in 1889, used the term in reference to Edward Bellamy''s Looking Backward: 2000 1887 and other works.