KMS client activation and product keys

To use Key Management Services (KMS), you need to have a KMS host available on your local network. Computers that activate with a KMS host need to have a specific product key. This key is sometimes referred to as the KMS client key, but it's formally known as a Microsoft Generic Volume License Key (GVLK). Computers that are running volume licensing editions of Windows Server and Windows client are, by default, KMS clients with no extra configuration needed as the relevant GVLK is already there.

Reference

https://learn.microsoft.com/en-us/windows-server/get-started/kms-client-activation-keys?tabs=windows1110ltsc%2Cwindows81%2Cserver2025%2Cversion1803