Business analysis glossary
Non-Functional Requirement
What it is
A non-functional requirement describes how well the system must work rather than what it does. Common categories are performance, security, availability, usability, accessibility, auditability and data retention. They are sometimes called quality attributes or constraints, and they often apply to the whole system rather than to a single feature.
Why it matters
A feature that works but is slow, insecure or unavailable still fails the user. Non-functional requirements are often forgotten until late, when they are expensive to fix. Asking about them early also surfaces cost: higher availability or stricter security can change the design and the price significantly.
Example
For the Orchard Health Clinics booking site: "Patient records shall be accessible only to authorised staff, every view shall be logged, and the booking page shall remain available at least 99.5 percent of the time each month." Each statement carries a measurable limit, so a tester can verify it with a tool or a log, and the business knows exactly what it is paying for.