The KMS server can then activate multiple client operating systems, depending on your Microsoft licensing agreement. This key is purchased from Microsoft and used to activate the KMS server deployed within your domain. The role of a KMS server needs to be installed on a Windows Server OS, which can then be activated (once) using a CSVLK, also known as the KMS Host Key.
It is used to activate the products which have been obtained through Volume Licensing.
How to Activate Windows using KMS Server.
