Space opera is one of the most widely known and longstanding subgenres of Science Fiction. E.E. "Doc" Smith (Lensman) is cited as one of the earliest examples, but Star Wars and Star Trek are far more known. Space opera involves stories of good v. evil, intergalactic war and politics, and good fighting evil. It's similar to westerns in many ways and the term space opera refers to its dramatic elements which can be like many soap operas with crisscrossing arcs and storylines and larger than life characters and emotions. It happens to be a favorite form of many SFF professionals.