This document defines science fiction and explores its key elements and subgenres. It begins by defining science fiction as fiction based on imagined future scientific or technological advances and major social or environmental changes. It contrasts science fiction with fantasy by noting science fiction deals with improbable possibilities based on scientific extrapolation, while fantasy involves plausible impossibilities. The document then examines common elements of science fiction like futuristic settings, advanced technology, and concern with outer space. It outlines several popular subgenres of science fiction like dystopian fiction, space opera, and military science fiction. In closing, it discusses why science fiction is studied, such as to enhance imagination, teach about technology, and encourage creativity.