Bidder (or proposer)

In the broad sense, the company or a group of companies, such as a consortium, that submits a bid in response to a RFP. A bidder could be a single party or a consortium of parties, each responsible for a specific element, such as constructing the infrastructure, supplying the equipment, or operating the business.
In strict terms, the bidder is only the company or companies that commit to form the project company or private partner (also known as the SPV), with other members of the bidding consortium acting potentially as the “nominated contractor”. The government normally contracts only with the company or companies that form the SPV, or with the SPV itself.