A ["Tester"] works with the ["Customer"] and an ["Analyst"] to define AcceptanceCriteria.
AcceptanceCriteria specify, as a collection of ["Scenario"], what needs to be achieved if the ["Behaviour"] of the ["Feature"] is to be considered finished.
AcceptanceCriteria are sometimes, incorrectly, referred to as SuccessCriteria. They differ in that in some cases AcceptanceCriteria can describe how the system fails as well as how it succeeds.