Non-functional requirements are requirements that describe how a solution needs to be built, installed, or operated to work optimally in an organization's environment. Where functional requirements define the "what," non-functional requirements address the "how." They relate to system quality, including topics such as reliability, scalability, and supportability.

If you are new to non-functional requirements, we recommend starting with our "101" on the topic: Non-Functional Requirements: What, Why, and How.