(a) "Goods" means all things which are moveable at the time of the sale or at the time the buyer takes possession, including goods not in existence at the time the transaction is entered into and goods which are furnished or used at the time of sale or subsequently in modernization, rehabilitation, repair, alteration, improvement or construction on real property so as to become a part thereof whether or not they are severable therefrom. "Goods" also includes merchandise certificates.
(b) "Merchandise certificate" means a writing issued by a seller not redeemable in cash and usable in its face amount in lieu of cash in exchange for goods and services.