A cost estimate, or a proposal to buy something, the value of which is kept secret from competitors until all such bids have been made.(noun)
Wiktionary.org : Text is available under the Creative Commons Attribution-ShareAlike License
Use "sealed bid" in a sentence
"Escambia County Administrator Bob McLaughlin on Tuesday said Escambia County commissioners have "ruined the integrity of the sealed bid system" used by the county to bid out construction contracts."