Section 250 - Definitions1. The term "real property" as used in this article includes the land itself above and under water, all buildings and other articles and structures, substructures and superstructures, erected upon, under or above, or affixed to the same; all wharves and piers, including the value of the right to collect wharfage, cranage or dockage thereon; all bridges, all telegraph lines, wires, poles and appurtenances; all supports and inclosures for electrical conductors and other appurtenances upon, above and underground; all surface, underground or elevated railroads, including the value of all franchises, rights or permission to construct, maintain or operate the same in, under, above, on or through, streets, highways, or public places; all railroad structures, substructures and superstructures, tracks and the iron thereon; branches, switches and other fixtures permitted or authorized to be made, laid or placed in, upon, above or under any public or private road, street or ground; all mains, pipes and tanks laid or placed in, upon, above or under any public or private street or place for conducting steam, heat, water, oil, electricity or any property, substance or product capable of transportation or conveyance therein or that is protected thereby, including the value of all franchises, rights, authority or permission to construct, maintain or operate, in, under, above, upon, or through, any streets, highways or public places, any mains, pipes, tanks, conduits or wires, with their appurtenances, for conducting water, steam, heat, light, power, gas, oil or other substance, or electricity or telegraphic, telephonic or other purposes; all trees and underwood growing upon land, and all mines, minerals, quarries and fossils in and under the same, except mines belonging to the state; and all the forms of housing which are adaptable to motivation by a power connected thereto or which may be propelled by a power within themselves and which are or can be used as a house or living abode or habitation of one or more persons, or for business, commercial or office purposes, either temporarily or permanently, and commonly called and hereafter referred to as "trailers"; except (1) transient trailers which have been located within the boundaries of a city, town or village for less than sixty days and (2) trailers which are for sale and which are not occupied. Said terms shall not include bulk milk tanks or coolers installed upon the farm to hold milk awaiting shipment to market. "Real property" also includes everything a conveyance or mortgage of which can be recorded as a conveyance or mortgage of real property under the laws of the state.2.(a) The term "mortgage" as used in this article includes every mortgage or deed of trust which imposes a lien on or affects the title to real property, notwithstanding that such property may form a part of the security for the debt or debts secured thereby. An assignment of rents to accrue from tenancies, subtenancies, leases or subleases of real property, within any city in the state having a population of one million or more, given as security for an indebtedness, shall be deemed a mortgage of real property for purposes of this article. Executory contracts for the sale of real property under which the vendee has or is entitled to possession shall be deemed to be mortgages for the purposes of this article and shall be taxable at the amount unpaid on such contracts. A contract or agreement by which the indebtedness secured by any mortgage is increased or added to, shall be deemed a mortgage of real property for the purpose of this article, and shall be taxable as such upon the amount of such increase or addition. Notwithstanding anything in this section or section two hundred fifty-five of this article to the contrary, a contract or agreement whereby the proceeds of any indebtedness secured by a mortgage of real property in any city in the state having a population of one million or more are used to reduce all or any part of a mortgagee's equity interest in a wraparound or similar mortgage of such real property shall be deemed a mortgage of real property for the purposes of this article and shall be taxable as such to the extent of the amount of such proceeds so used, without regard to whether the aggregate amount of indebtedness secured by mortgages of such real property is increased or added to.(b) Where all or part of the indebtedness secured by a mortgage of real property within any city in the state having a population of one million or more has been paid and new funds are advanced or re-advanced which are to be secured by such mortgage, the contract or agreement by which such funds are advanced or re-advanced shall be deemed a mortgage of real property for purposes of this article, and shall be taxable as such upon the amount of such new funds, except as otherwise provided in section two hundred fifty-three-b of this article.3. The term "tax district" as used in this article means a city or town.