While there have been a lot of different descriptions of science fiction, they usually mention:
- characters reacting to changes in science and technology
- ideas about possible future events based on our understanding of the real world
Science fiction tries to use ‘realistic imagination’ - amazing inventions, new worlds, and alternative realities (Ready Player One, Star Trek, The Maze Runner). Sc-fi stories also try to explain how these things came to be. This is different from fantasy, which uses magic, mythical creatures and supernatural powers (Harry Potter, The Lord of the Rings, Superman).
Some stories mix science fiction, fantasy, and supernatural elements. For example, Star Wars mixes science fiction standards like spaceships and alien worlds with magical elements like The Force. You can always call these stories speculative fiction, which is a very handy catch-all!