Test Case Design is the process of creating a set of conditions or variables to determine if a software application behaves as expected. It involves identifying specific scenarios that the software should handle, including both typical and edge cases. Each test case outlines the input, execution steps, and expected outcomes, ensuring comprehensive coverage of the application's functionality. Effective test case design helps in identifying defects early in the development process, improving software quality. It also facilitates better communication among team members, as clear test cases provide a shared understanding of what needs to be tested. This practice is essential for successful software testing and quality assurance.