Nonfunctional Requirements

Nonfunctional Requirements (NFR), describe system attributes such as security, reliability, maintainability, scalability, and usability (often referred to as the _qualities_ or _ilities_). They can also be constraints or restrictions on the design of the system. Nonfunctional Requirements are persistent qualities and constraints, and unlike functional requirements, are typically revisited as part of the _Definition of Done_. NFRs exist at Team, Program and Portfolio Backlog levels.