There are several of types of specifications that are commonly used. The following are some of the most common forms:

• Performance Specification—A type of specification in which the goods and/or services are described in terms of required performance. They may include such details as required power, strength of material, test methods, and standards of acceptability and recommended practices.¹  Performance specifications define the task or desired result by focusing on what is to be achieved (e.g., truck or airplane). ²
• Design Specification—These are detailed descriptions of a good or service, including such things as details of construction or production, dimensions, chemical composition, physical properties, materials, ingredients and other details needed for the provider to produce an item of minimum acceptability. Design specifications are usually required for construction projects and custom produced items and for many services.³Architects and engineers typically prepare design specifications for construction and manufactured products (e.g., buildings, highways, or other public works projects).
• Combination Specification—This type of specification includes elements of both design and performance specifications.⁴
• Brand Name or Equal—This type of specification is used to describe a commodity of a fairly common nature. It states a detailed  description and a manufacturer and catalog or model number which meets the description and has been determined to be acceptable.⁵Competition among brands is usually attained by specifying “brand A or equal” in the specification.⁶
• Industry Standard—In this type of specification, all goods made to an industry standard are identical, regardless of manufacturer, and will result in acquisition of goods of uniform quality. An example is the UIL standard for electrical products.⁷