George Lucas is a toy-maker as much as he is a director, which explains why we know what to call half the things in the Star Wars universe.
AT-ATs, the Sith, A-Wings, and Ewoks. We know what they are—through the prequels, the toys, and the extended universe—but they’re absolutely never called those things by name in the original films. For that matter, the existence of the “light” side was a total inference on our part, since only the dark side was mentioned. And before Darth was a title for Really Evil Guys, it was just Vader’s first name.
Star Wars also suffers from the Casablanca problem of being perpetually misquoted but hey, “No, I am your father” doesn’t have the same snap to it.
But you’re a fan, so you already knew all that, right?