In Windows, build numbers are unique identifiers assigned to each specific update or revision made to the operating system. They are crucial for identifying the exact state of your Windows installation, troubleshooting issues, and ensuring software or driver compatibility. Build numbers help IT professionals and support teams determine the precise version of Windows you're running, which is essential when diagnosing problems or ensuring that applications and drivers are compatible with your version of Windows. To find your build number, press Win + R, type winver, and press Enter; the build number is listed under the version number in the 'About Windows' box.