From the Wikipedia at
"A contract manufacturer ("CM") is a firm that manufactures components or products for another "hiring" firm. Many industries utilize this process, especially the aerospace, defense, computer, semiconductor, energy, medical, personal care, and automotive fields. Some types of contract manufacturing include CNC machining, complex assembly, aluminum die casting, grinding, broaching, gears, and forging.
In a contract manufacturing business model, the hiring firm - typically an OEM - approaches the contract manufacturer with a design or formula. The contract manufacturer will quote the parts based on processes, labor, tooling, and material costs. Typically an OEM will request quotes from multiple CMs. After the bidding process is complete, the hiring firm will select a source, and then, for the agreed-upon price, the CM acts as the hiring firm's factory, producing and shipping units of the design on behalf of the hiring firm.
Many well-known companies use contract manufacturing as an alternative to operating and maintaining their own factories."