The central element of what is purchased is called the "core," and anything bought on top of that is called what?

value added product

Explanation:

Core services are basic things that customers want from products they purchase. Value-added services differentiate the organization from competitors . The value added products are defined as follows: A change in the physical state or form of the product (such as milling wheat into flour or making strawberries into jam). The production of a product in a manner that enhances its value, as demonstrated through a business plan (such as organically produced products).The value added products build relationships that bind customers to the firm in a positive way.