Diegetic and Non-Diegetic

The terms diegetic and non-diegetic show up all kinds of places. In literary theory, I'm assuming in theater stuff that shows up. But my big familiarity with it is in cinema studies where it's a huge thing. So when we talk about a character's feelings for another character, we're analyzing the diegetic world. Do you have anything to any additional diegetic information? Not particularly.