A construction bid is a formal price proposal from a contractor to an owner (or general contractor, in the case of subcontractor bids) to perform a defined scope of work for a stated price. Bids are typically prepared in response to an invitation to bid (ITB) accompanied by a drawing set, specifications, and bid documents.
A bid differs from an estimate in two ways. First, a bid is firm: once submitted and accepted, it becomes the contract price. An estimate is informational and revisable. Second, a bid is competitive: the owner typically receives multiple bids and selects one, while estimates are usually one-on-one. Hard bids include not only price but also schedule, exclusions, alternates, value engineering options, and required insurance / bonding documentation.