Non-functional requirements
Also called: NFRs, Quality attributes
Requirements about how well a system works, such as scale, latency, availability and consistency, rather than what it does.
Definition
Functional requirements list features; non-functional requirements set the qualities those features must have: how many users, how fast, how reliable, how fresh the data must be, how secure. In system design they drive most decisions, because the same features at a thousand and at a hundred million users need very different designs.
In practice
"The feed loads in under 200 ms for 10 million daily users, and a new post may appear a few seconds late."
Learn it in context
Lessons that use this term.