In this chapter:
(1) "Auction company" has the meaning assigned by Section 1802.001, Occupations Code.
(2) "Residential real property" means:
(A) a single-family house;
(B) a duplex, triplex, or quadraplex; or
(C) a unit in a multiunit residential structure in which title to an individual unit is transferred to the owner of the unit under a condominium or cooperative system.
(3) "Security instrument," "substitute trustee," and "trustee" have the meanings assigned by Section 51.0001, Property Code.