These are the requirements that express what a software solution should do to solve some customer problem. Traditionally functional requirements describe what tangible outputs are produced by a software solution for a given suite of inputs. Functional requirements also include behavior rules, standards, policies, and other factors from the customer problem space that affect what the software needs to do to the inputs in order to provide the specified outputs. Contrast: nonfunctional requirements that address how the application should execute.
The functionality we desire of a problem solution.
Functional Requirements are one type of Information Technology Security (ITS) requirement identified under the Common Criteria (CC). These requirements define the security behaviour of the Information Technology (IT) product/system and answer the question "What does the product do?"
Functional requirements define the internal workings of the : that is, the calculations, technical details, data manipulation and processing, and other specific functionality that show how the use cases are to be satisfied. They are supported by non-functional requirements, which impose constraints on the design or implementation (such as performance requirements, security, quality standards, or design constraints).