A Windows 8.1 Product Key is a 25-character code used to activate and validate the authenticity of the Windows 8.1 operating system. This key ensures the software is genuine and grants access to all the features of the edition you’ve installed, such as improved multitasking, the Start screen, and enhanced security options.

The product key follows the format: XXXXX-XXXXX-XXXXX-XXXXX-XXXXX.

It is required during installation or when making significant hardware changes. The key is usually found on the packaging or provided via digital purchase.