A test case is a set of conditions or variables under which a tester will determine whether a system or component meets the specified requirements. It is a tool that is used to verify that the system or component is functioning correctly and meets the specified requirements. Test cases are an important part of the testing process, as they provide a clear and structured approach for verifying the functionality of a system or component. They are often used in conjunction with test plans and test scripts, which provide additional guidance and detail about the testing process.