Non-functional requirement

Non-functional requirement is a type of requirement that describes the performance or quality attributes a solution must meet. Non-functional requirements are usually measurable and act as constraints on the design of a solution as a whole.

Definitions

According to the BABOK Guide (3rd edition),

Non-functional requirement. A type of requirement that describes the performance or quality attributes a solution must meet. Non-functional requirements are usually measurable and act as constraints on the design of a solution as a whole.