casual: 잘 있어 · formal: 안녕히 계십시오
goodbye (to someone who is staying)
Example
사장님, 잘 먹었습니다. 안녕히 계세요.
Thank you for the meal. Goodbye!
Word parts
안 peace+녕 peace
안녕히 (peacefully) + 계세요 (please stay) — 'stay in peace'; said by the one leaving.
Good to know
Used when YOU are leaving and the other person stays, e.g. leaving a shop or someone's home.