You can still buy legitimate, unused Office 2016 keys from authorized resellers or surplus software markets for as little as $20–$50 USD (Home & Student edition). These keys:
A KMS activator creates a fake KMS server (often emulated within your own computer's loopback adapter). It forces your copy of Office 2016 to connect to this fake server, which then approves the activation. This tricks Office into thinking it is part of a legitimate volume licensing network. index of kms activator office 2016 better