Section 1. In this chapter, except when the context otherwise requires, the following words shall have the following meanings:—

''Dealer'', any person who is engaged principally in the business of buying, selling, or exchanging vehicles and who has a place of business within the commonwealth.

''Identifying number'', the numbers, and letters if any, designated by the registrar for the purpose of identifying the vehicle.

''Implement of husbandry'', a vehicle designed and adapted primarily for agricultural, horticultural or livestock raising operations or for lifting or carrying an implement of husbandry.

''Motor vehicles'' or ''Vehicles'', all vehicles constructed and designed for propulsion by power other than muscular power including such vehicles when pulled or towed by another motor vehicle, except railroad and railway cars, vehicles operated by the system known as trolley motor or trackless trolley under chapter one hundred and sixty-three or section ten of chapter five hundred and forty-four of the acts of nineteen hundred and forty-seven, vehicles running only upon rails or tracks, vehicles used for other purposes than the transportation of property and incapable of being driven at a speed exceeding twelve miles per hour and which are used exclusively for the building, repair and maintenance of highways or designed especially for use elsewhere than on the travelled part of ways, wheelchairs owned and operated by invalids and vehicles which are operated or guided by a person on foot. The definition of ''Motor vehicles'' shall not include motorized bicycles. In doubtful cases, the registrar may determine whether or not any particular vehicle is a motor vehicle as herein defined. If he determines that it should be so classified, he may require that it be registered under this chapter, but such determination shall not be admissible as evidence in any action at law arising out of the use or operation of such vehicle previous to such determination.

''Owner'', a person, other than a lien holder, having title to a vehicle. The term includes a person entitled to use and possession of a vehicle subject to a security interest in another person, but excludes a lessee under a lease not intended as security and a bailee of any description.

''Registrar'', the registrar of motor vehicles or his duly authorized agents.

''Special mobile equipment'', vehicles exempt from registration by the registrar under the provisions of section nine of chapter ninety.

''Supporting documents'', any written document or form submitted to the registrar of motor vehicles as evidence of ownership, liens or any other information required under the provisions of this chapter.

''Total loss salvage motor vehicle'', a motor vehicle which has been stolen and unrecovered or which has been wrecked, destroyed or damaged by collision, fire, water, or other occurrence to such an extent that the owner or if the vehicle was insured, the insurer, considers it uneconomical to repair the vehicle and because of this, the vehicle is not repaired by or for the person who owned the vehicle at the time of the event resulting in such damage.

''Trailer'', any vehicle or object on wheels and having no motive power of its own, but which is drawn by, or used in combination with, a motor vehicle. It shall not include a pole dolly or pole dickey, so-called, nor a pair of wheels commonly used as an implement for other purposes than transportation, nor a portable or collapsible dolly carried in a tow truck for the purpose of transporting registered disabled vehicles to a place of safety or a place equipped for the repair of such disabled vehicles, but not including the transportation of vehicles which are not disabled, nor farm machinery or implements when used in connection with the operation of a farm or estate, nor any vehicle when towed behind a farm tractor and used in connection with the operation of a farm or estate.