A Test Scenario is generally a one line statement describing a feature of application to be tested. It is used for end to end testing of a feature and is generally derived from the use cases.
A single test scenario can cover one or more test cases i.e. it has a one to many relationship with test cases.
Scenario testing is a type of testing carried out using scenarios derived from the use cases. Using scenario testing, complex application-logic can be tested using easy to evaluate test scenarios.
Some advantages of test scenarios are -