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

''Commissioner'', the commissioner of banks.

''Finance charge'', the cost of credit determined in accordance with the provisions of section four of chapter one hundred and forty D.

''Holder'', the retail seller of the motor vehicle under or subject to a retail instalment contract, or, if the contract is purchased by a financing agency or other assignee, the sales finance company or other assignee.

''Motor vehicle'', any self-propelled, motored device in, upon or by which any person is, or may be, transported or drawn upon a highway and which is used or bought for use primarily for personal, family or household purposes. The term does not include self-propelled tractors, trucks other than those purchased for personal or family non-business use, all commercial trailers and semitrailers, buses, earth-moving and construction machinery or equipment, power shovels, road building machinery or equipment, implements of husbandry and other agricultural machinery or equipment, or machinery or equipment not designed primarily for highway transportation but which may incidentally transport persons on a highway, or devices which move upon or are guided by a track, or travel through the air.

''Retail buyer'' or ''buyer'', a person who buys or agrees to buy a motor vehicle from a retail seller for use primarily for personal, family or household purposes and who executes a retail instalment contract in connection therewith, or any legal successor in interest to such person, notwithstanding that he may have entered into one or more extension or refinancing agreements.

''Retail instalment contract'' or ''contract'', an agreement, signed by the buyer in this state, pursuant to which the title to, the property in or a lien upon a motor vehicle, which is the subject matter of a retail instalment sale, is retained or taken by a retail seller from a retail buyer as security, in whole or in part, for the buyer's obligation. The term includes a chattel mortgage, a conditional sales contract and a contract for the bailment or leasing of a motor vehicle by which the bailee or lessee contracts to pay as compensation for its use a sum substantially equivalent to or in excess of its value and by which it is agreed that the bailee or lessee is bound to become, or has the option of becoming, the owner of the motor vehicle upon full compliance with the terms of the contract.

''Retail instalment sale'' or ''sale'', a sale of a motor vehicle by a retail seller to a retail buyer for a total sale price payable in two or more instalments, payment of which is secured by a retail instalment contract.

''Retail seller'' or ''seller'', a person who sells a motor vehicle to a retail buyer under or subject to a retail instalment contract.

''Sales finance company'', (1) a bank as defined in section one of chapter one hundred and sixty-seven, a national banking association, (2) any person engaged, in whole or in part, in the business of purchasing retail instalment contracts from one or more retail sellers and (3) a retail seller engaged, in whole or in part, in the business of holding retail instalment contracts acquired from retail buyers. The term ''sales finance company'' does not include the pledgee of an aggregate number of such contracts to secure a bona fide loan thereon.