Functional requirements define the system’s precise functionality, describing what the system can and cannot accomplish.
Non-functional requirements, on the other hand, specify how the system shall carry out its functions. It defines the accessibility, dependability, capacity, usefulness, maintainability, and security of a system. Non-functional requirements are those that impact the user experience by describing system behaviour, features, and general characteristics.
The system’s basic functioning is unaffected by non-functional needs. Even if the non-functional criteria are not satisfied, the system will continue to serve its primary purpose.