A product key is a 25-character code that's required to activate Microsoft Office 2016 Professional Plus. It's usually provided with the purchase of the software or can be found in the confirmation email if you bought it online.

This is the most common "working" method found on GitHub. Scripts (often associated with the massgravel or similar projects) redirect your PC’s activation attempt to a non-Microsoft KMS server.

GitHub repositories and Gists typically provide different methods to bypass or manage activation:

How do I activate Microsoft Office 2016 Professional Plus without a product key? A: You can try using the free trial version or consider purchasing a legitimate product key from Microsoft or authorized retailers.