PDAs

When you created an associated token account , you actually created a PDA -

https://github.com/solana-labs/solana-program-library/blob/master/associated-token-account/program/src/lib.rs#L71

JS - https://github.com/solana-labs/solana-program-library/blob/ab830053c59c9c35bc3a727703aacf40c1215132/token/js/src/state/mint.ts#L171