Meaning of the word "sealed deal" in English

What does "sealed deal" mean in English? Explore the meaning, pronunciation, and specific usage of this word with Lingoland.

sealed deal

US /siːld diːl/
UK /siːld diːl/

Phrase

an agreement or transaction that has been finalized and cannot be changed

Example:
After weeks of negotiations, the contract is a sealed deal.
Once you sign the papers, it's a sealed deal.