Criteria translate a broad goal into observable behavior, constraints or evidence. They can describe expected user outcomes, error handling, performance, compatibility or the exact tests that must pass.
A useful criterion is clear enough for an implementer and reviewer to reach the same conclusion. Vague phrases such as 'works well' should be replaced with measurable conditions tied to the actual requirement.
ELI5
An acceptance criterion is a clear condition that work must meet before it counts as complete. It describes an observable result, so the builder and reviewer can agree on what success means.
For example, a search feature might require that a user can find a product by its full name and receive results within two seconds. Saying only that the search should be good would be too vague to test reliably.
What makes an acceptance criterion useful?
It should be specific, observable, relevant to the requirement and understandable to both implementers and reviewers.
Can one task have several acceptance criteria?
Yes. Separate criteria can cover normal behavior, errors, security, compatibility and other required outcomes.
