mortgage
(1) The term “mortgage” means a first mortgage on real estate in fee simple, or on the interest of either the lessor or lessee thereof (A) under a lease for not less than ninety-nine years which is renewable or (B) under a lease having a period of not less than fifty years to run from the date the mortgage was executed, upon which there is located or upon which there is to be constructed a building or buildings designed principally for residential use, or upon which there is located or to be constructed facilities for manufactured homes, and the term “first mortgage” means such classes of first liens as are commonly given to secure advances (including but not being limited to advances during construction) on, or the unpaid purchase price of, real estate under the laws of the State, in which the real estate is located, together with the credit instrument or instruments, if any, secured thereby, and may be in the form of trust mortgages or mortgage indentures or deeds of trust securing notes, bonds, or other credit instruments.