The exposition means it is a literary device used to introduce background information about events, settings, characters etc.
for an example The exposition in star wars is the opening title sequence that gives information about the past events to the viewers. The crawling text on the screen at the beginning of each part gives the audience every piece of information they need to understand the upcoming events in the film. The opening lines usually begin like this: “A long time ago in a galaxy far away, far away…”
