Test-Driven Development (TDD) is a software development approach where developers write tests for their code before actually writing the code itself. This means that for every new feature or function, a test is created first to define what the code should do. By doing this, developers ensure that they have a clear understanding of the requirements and can catch errors early in the process. Once the tests are written, developers then write the minimum amount of code needed to pass those tests. This cycle of writing a test, coding, and then refactoring continues until the software is complete. TDD helps improve code quality and maintainability, making it easier to adapt to changes in the future.