TDD stands for Test-Driven Development. It is a software development process in which tests are written first, before any code is written. The tests are written to define the desired behavior of the code that will be written. Once the tests are written, the code is written to pass the tests. This helps to ensure that the code does what it is supposed to do, and that it works correctly. TDD is particularly useful for JavaScript development, as it helps to ensure that the code runs properly on different browsers and devices.