"Red-Green-Refactor" is a software development practice used in Test-Driven Development (TDD). It consists of three main steps: first, you write a test that fails (Red), indicating that the desired functionality is not yet implemented. This step helps clarify what needs to be developed. Next, you write the minimum amount of code necessary to make the test pass (Green). Once the test is passing, you can refactor the code to improve its structure and readability without changing its behavior. This cycle encourages continuous improvement and ensures that the codebase remains robust and maintainable.