ELI5 Debt Ceiling - what's the trillion dollar coin?

Why do we have a debt ceiling? What used to happen before it was invented? Do other countries have one? What happened in 2011 and why did it involve Apple? What was the trillion dollar coin and why are people talking about it again?   ... We explain like i'm five!   Thank you to the r/explainlikeimfive community and in particular the following users whose questions and comments formed the basis of this discussion: the_walking_deaf, bolshevikmuppet, lobsang_ludd, bossgalaga, the_cleric, buzzyness and chrisfartwick To the ELI5 community that has supported us so far, thanks for all your feedback and comments. Join us on Twitter: https://www.twitter.com/eli5ThePodcast/ or send us an e-mail: [email protected]