Test-Driven Development (TDD) is a software development approach where tests are written before the actual code. This method encourages developers to define the desired functionality of their code upfront, ensuring that the software meets its requirements from the start. By focusing on tests first, developers can create more reliable and maintainable code. In TDD, the process typically follows a cycle known as Red-Green-Refactor. First, a failing test is written (Red), then the code is implemented to pass the test (Green), and finally, the code is improved without changing its behavior (Refactor). This cycle helps maintain high code quality throughout the development process.