Specifications

Specifications are the most detailed method of describing requirements. Various types of design specifications are the detailed descriptions of the materials, parts, and components to be used in making a product. Hence, they are the descriptions that tell the seller exactly what the buyer wants to purchase.

Source: Dobler, D.W., & Burt, D.N. (1996). Purchasing and Supply Management. (6th ed.). New York: McGraw Hill.