A genre of literature that involves speculative or futuristic concepts, often based on advanced science and technology, space exploration, time travel, parallel universes and extraterrestrial life. While it may overlap with fantasy books in terms of imaginative and extraordinary elements, it distinctly sets itself apart by grounding its narratives in scientific theories and principles. This category does not typically encompass biographies, unless they are of significant figures in the field of science fiction. It is a subcategory of the broader term "books."