Referring to things that happen "behind the camera", the real-life reasons for how/why a TV/film/book/comic turned out the way it did
Referring to events that aren't part of the end product (TV/film/book etc...) that influence the plot, characters or other aspects of the final product, often referred to as "out-of-universe" explanations.
Question: Why were there no interior shots of spaceship X?
In-universe answer: Alien race Y was secretive and didn't allow strangers on-board.
Behind-the-scenes answer: The interior shots were too costly and the budget wouldn't stretch to it.