Sci-fiSci-fi is an abbreviation for science fiction. It was invented in the 1950s by Forrest J. Ackerman as a jokey pun on hi-fi. Many science fiction fans hated the word, considering it a trashy gimmick.
The "official" abbreviation for science fiction is SF, but journalists got hold of the word "sci-fi" and it entered popular usage. Despite its almost universal usage, many "serious" science fiction fans still cringe when they hear the word.