Final answer:
Functional requirements outline the specific actions or tasks that a system must be able to perform and are a critical component of system development. They differ from general, user, and nonfunctional requirements, which cover broader needs, user perspectives, and performance-related attributes, respectively.
Step-by-step explanation:
The description of what functions the system must perform (is required to do) is called functional requirements. Functional requirements specify actions or tasks that a system or component must be able to perform. These requirements are crucial to the development process as they define the expectations and capabilities of the system from the perspective of system functionality.
Other types of requirements include general requirements, which may be broader and less detailed, user requirements, which focus on the needs and wants of the end-users, and nonfunctional requirements, which address the system's performance, usability, reliability, and other attributes that do not relate directly to specific functionalities.