Information the audience needs - backstory, rules, context - and the craft of hiding its delivery.
Exposition is necessary cargo: who these people are, how the heist works, what the prophecy says. The failure mode is delivering it as delivery - two characters telling each other things they both already know ('As you know, brother…').
The classic solutions: make someone need the information now, attach it to conflict, or make the audience want it before you hand it over. Information that costs a character something to reveal never feels like exposition.
Plan with 30+ story frameworks, write your screenplay or novel, and let Quill coach every beat - it guides and never writes. Free account, no card.