During bid preparation the estimator breaks the job into scopes and sends RFQs to the vendors and subs who can price each one. The returned quotes become line items in the estimate, usually with the estimator's markup applied.
The practical failure mode is tracking: RFQs go out from one inbox, replies land in another, and on bid night nobody is sure which vendor actually responded or which number was final. Keeping RFQs and their replies attached to the project record, not to whoever's inbox sent them, is one of the main reasons estimating teams adopt bid management software.
RFQ is distinct from RFI (request for information): an RFI asks the designer to clarify the documents; an RFQ asks a vendor to commit to a price.