Undercoating is a protective layer that is applied to the underside of a vehicle to protect it from rust and other damage caused by road debris. Some of the synonyms for undercoating include rust protection, undercarriage coating, underbody spray, and rust inhibitor. Rust protection is a coating that helps prevent rust from forming on metal surfaces. Undercarriage coating is a layer of protective material that is applied to the underside of a vehicle. Underbody spray is a term used to describe a spray that is applied to the undercarriage of a vehicle to protect it from the elements. Rust inhibitor is a type of coating that prevents rust from forming on metal surfaces.