[provide a list of contractual or task level assumptions and/or constraints that are preconditions to preparation of the frd. It provides a single reliable source of. A functional requirements document (frd)—also known as a functional requirements specification, functional specification, or functional specification document—is a more. A functional specification document (fsd), also known as a functional requirements document (frd), is considered by many project management and software. Writing a functional requirements document (frd) is an essential step in the software development process.