Non-functional requirement

In systems and software engineering, a non-functional requirement specifies criteria for judging how a system operates overall, rather than describing a specific behavior the system must perform, and is often called a quality attribute or architectural characteristic. Functional requirements describe what a system must do, phrased as the system shall do something, while non-functional requirements describe how the system must be, phrased as the system shall be something. One illustrative example is that displaying the number of records in a database is a functional requirement, while how current that number must be is a non-functional one. Common examples include performance and response time, security, reliability, scalability, maintainability, usability, accessibility, availability, compatibility and fault tolerance. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/