The Business Requirement Document (BRD) describes the high-level business needs, while the Functional Requirement Document (FRD) describes the functions that are needed to meet the business need. The functional requirements document (FRD) is a list of how an application needs to work. It does the same thing that a contract does. The development teams agree to give the features that were asked for. The client agrees that the product will be good enough if it can do what is written in the FRD.