California Code, Vehicle Code - VEH § 615

(a) A “tow truck” is a motor vehicle which has been altered or designed and equipped for, and primarily used in the business of, transporting vehicles by means of a crane, hoist, tow bar, tow line, or dolly or is otherwise primarily used to render assistance to other vehicles. A “roll-back carrier” designed to carry up to two vehicles is also a tow truck. A trailer for hire that is being used to transport a vehicle is a tow truck. “Tow truck” does not include an automobile dismantlers' tow vehicle or a repossessor's tow vehicle.

(b) “Repossessor's tow vehicle” means a tow vehicle which is registered to a repossessor licensed or registered pursuant to Chapter 11 (commencing with Section 7500) of Division 3 of the Business and Professions Code that is used exclusively in the course of the repossession business.

(c) “Automobile dismantlers' tow vehicle” means a tow vehicle which is registered by an automobile dismantler licensed pursuant to Chapter 3 (commencing with Section 11500) of Division 5 and which is used exclusively to tow vehicles owned by that automobile dismantler in the course of the automobile dismantling business.