In this subtitle the following words have the meanings indicated unless otherwise apparent from context. “Improvements” includes every newly constructed private dwelling unit, and fixture and structure which is made a part of a newly constructed private dwelling unit at the time of construction by any building contractor or subcontractor. “Purchaser” means the original purchaser of improved realty, and the heirs and personal representatives of the original purchaser. “Realty” includes both freehold estates and redeemable leasehold estates. “Vendor” means any person engaged in the business of erecting or otherwise creating an improvement on realty, or to whom a completed improvement has been granted for resale in the course of his business.