What are functional versus non-functional requirements?
Functional requirements refer to the behavior of the systems (e.g. “I want to have a specific action come from the system itself.”)
Non-functional requirements are related to the operation of the system as a whole. For example, a non-functional requirement might be, “We need to get a certain level of performance coming out of the application, regardless of the individual requirements themselves.” Or, “We need to maintain a certain amount of uptime for the website.”
So, functional requirements refer to individual actions coming from the system. Non-functional requirements are related to the overall system itself, and how the overall system performs.