A more thorough explanation:

A design specification is a document that outlines what one party, such as a seller, will do for another party, such as a buyer. It is often included as a contractual provision or exhibit in a statement of work.

The statement of work typically covers terms such as inspection and acceptance, quality-assurance requirements, packing and marking, data requirements, and training. There are two types of specifications in a statement of work: performance specifications and design specifications.

Performance specifications establish the minimum requirements for items to be supplied, while design specifications establish the methods to be used in meeting those minimum requirements.

For example, a company may hire a contractor to build a website. The statement of work would include a design specification outlining the specific features and functionality the website must have, such as a shopping cart and a contact form. The performance specification would outline the minimum requirements for the website's speed, security, and accessibility.