Science fiction (sometimes shortened to sci-fi or SF) is a genre of speculative fiction that typically deals with imaginative and futuristic concepts such as advanced science and technology, space exploration, time travel, parallel universes, and extraterrestrial life. It has been called the "literature of ideas", and often explores the potential consequences of scientific, social, and technological innovations.Science fiction, whose roots go back to ancient times, is related to fantasy, horror, and superhero fiction, and contains many subgenres. Its exact definition has long been disputed among authors, critics, scholars, and readers. Science fiction literature, film, television, and other media have become popular and influential over much of the world. Besides providing entertainment, it can also criticize present-day society, and is often said to inspire a "sense of wonder".