A KMS Activator (Key Management Service Activator) is a tool used to activate Microsoft products such as Windows and Office without the need for a genuine license key. It works by emulating a KMS server on your local machine, which tricks the Microsoft software into thinking it is communicating with a legitimate KMS server. This method is often used for educational purposes or in organizations with volume licensing agreements. However, using such tools to bypass licensing restrictions can violate Microsoft’s terms of service and may lead to legal issues.