A test case is a set of conditions or variables under which a tester will determine whether an application, software system or one of its features is working or not .
test-case is a step by step procedure to validate either application is working as user requirement or not.
A test case is a documentation which specifies input values, expected output and the preconditions for executing the test.
it is in detail document which contains all possible combination with nevigation steps along with valid input datas which needs to be followed by test engineers to conduct optimized testing.
In just one line ---- Sequential Elaborated Executable form of Requirement is known as Test cases