What is a test cases and what is the purpose of a test cases?

Test Case:

A test case is a document that describes step by step process how to test the application.

Test case includes:

Test case ID, Step Name, Step Description, Test Data, Expected Output, Actual Output, Pass/Fail and comments.

The purposes of the test case are:
Ø To achieve the 100% RM coverage

Ø Reduce the defect in the application

Ø Verifying standards guideline

Ø Validating users need