Space opera is a real subset of science fiction. According to sciencefiction.com, “Space opera is a genre of science fiction literature, and the term can also be applied to movies and TV programs. The genre has almost no relationship to the opera music form, except for the similarity of grand scope and dramatic intensity. Typically, space opera occurs on a galactic scale, has multiple types of spacecraft, from speedy corvettes to battleships capable of destroying planets. There is plenty of action and adventure in space opera.”
Well-known Space operas include Doctor Who, The Foundation series, and the Ancillary Justice series (which I just read and would highly recommend).