| The method of providing traction to any of the wheels of a vehicle, as conditions require. Depending on the system, it may be full-time or part-time. | |
| Parts equipment manufacturing that is not original equipment from the factory. | |
| A device attached to a mechanically driven cooling fan that allows the fan to freewheel when the engine is cold and the vehicle is driven at speed. | |
| The hydraulic fluid used to transmit hydraulic pressure through the brake lines in a brake system. |