What is a functional requirement?

A functional requirement is a specification that outlines the specific behaviors or functions that a system must perform. It describes what the system should do in terms of actions or tasks, detailing the interactions between the system and its users, as well as how the system handles input and output. This includes use cases, business rules, and descriptions of system operations that allow stakeholders to understand exactly what the system should accomplish to meet business needs.

For example, a functional requirement might specify that a system must allow users to create an account or that it should process a payment when given valid credit card information. These requirements are essential in ensuring that the software meets the intended goals and fulfills user expectations.

In contrast, the other types of requirements mentioned in the options focus on different aspects of a system. Usability features relate to how easy it is for users to interact with the system and are more aligned with user interface design rather than functional specifications. Performance criteria deal with the speed, responsiveness, and efficiency of the system, while system limits specify constraints or boundaries within which the system operates, such as data capacity or processing limits. These do not directly address the specific operations that the system is designed to perform, which makes the definition provided by the correct answer distinct and critical for the overall understanding