In-universe

Referring to Lord Voldemort as the most feared person in the world is an in-universe classification in the Harry Potter series.

And in Mass Effect 2, you can find a secret dossier on the synthetic Geth sniper called Legion, which was created solely to preserve its species. This dossier shows that this apparently serious Geth spends a lot of processing time playing video games — ranging from playing as a Level 612 Ardat-Yakshi Necromancer in Galaxy of Fantasy, an in-universe MMO with over eleven billion players, to being a max-scoring sniper in Code of Honor: Medal of Duty.

The Star Wars novels, comics, video games, television series, and radio shows created between 1977 and 2012 all constitute an original Expanded Universe (EU) of in-universe history and lore set within the same transmedia franchise.