(a) A mortgage is a contract by which specific property, including an estate for years in real property, is hypothecated for the performance of an act, without the necessity of a change of possession.
(b) For purposes of Sections 2924 to 2924h, inclusive, “mortgage” also means any security device or instrument, other than a deed of trust, that confers a power of sale affecting real property or an estate for years therein, to be exercised after breach of the obligation so secured, including a real property sales contract, as defined in Section 2985, which contains such a provision.