The FAR treats what the market already sells differently from what is made only for government. One path into the definition of a commercial product is a product, other than real property, of a type customarily used by the general public or by nongovernmental entities for purposes other than governmental purposes 1.
"Purposes other than governmental purposes" has a plain meaning in Part 12: purposes that are not unique to a government 2.
Services have their own definition. One path covers services of a type offered and sold competitively in substantial quantities in the commercial marketplace, based on established catalog or market prices for specific tasks or outcomes, and under standard commercial terms and conditions 3.
What changes when the buy is commercial
Agencies are told to acquire commercial products, commercial services or nondevelopmental items when they are available to meet the agency's needs 4.
When a buy meets the definitions, FAR Part 12 is used for it 5. Where another part of the FAR is inconsistent with Part 12, Part 12 takes precedence for commercial buys 6.
The clause list shrinks. Commercial contracts are to include, to the maximum extent practicable, only certain clauses 7. One kind the FAR allows is a clause determined to be consistent with customary commercial practice 8.
The core terms arrive as one clause, FAR 52.212-4, prescribed at FAR 12.301(b)(3) 9. Under it, changes in the terms and conditions may be made only by written agreement of the parties 10.
The same clause still reserves the government's right to terminate the contract, or any part of it, for its sole convenience 11.
Contract type narrows too. The contracting officer uses firm-fixed-price or fixed-price with economic price adjustment contracts for commercial products and commercial services, except as FAR 12.207(b) provides 12.
The preference reaches suppliers. Where FAR 52.244-6 is in a contract, the contractor must, to the maximum extent practicable, incorporate commercial products, commercial services or nondevelopmental items as components, and require its subcontractors at all tiers to do the same 13.
Worked example. A civilian agency buys office chairs that are sold in stores, and separately buys a test fixture built only to its own drawings. Contractor F, which bids both, expects the chair order to carry the commercial terms clause and a short clause list, and reads the fixture solicitation's full Section I before pricing.
Indented paragraphs are invented worked examples. Tool links open Bids2Bank and need a free account.