Science fiction (often shortened to sci-fi or abbreviated SF) is the genre of speculative fiction that imagines advanced and futuristic scientific or technological progress. The elements of science fiction have evolved over time: from space exploration, extraterrestrial life, time travel, and robotics; to parallel universes, dystopian societies, and biological manipulations; and, most lately, to information technology, transhumanism (and posthumanism), and environmental challenges. Science fiction often specifically explores human responses to the consequences of these types of projected or imagined scientific advances.
The precise definition of science fiction has long been disputed among authors, critics, scholars, and readers. It contains many subgenres, including hard science fiction, which emphasizes scientific accuracy, and soft science fiction, which focuses on social sciences. Other notable subgenres are cyberpunk, which explores the interface between technology and society; climate fiction, which addresses environmental issues; and space opera, which emphasizes pure adventure in a universe in which space travel is common.