Overview:

Skype for Business hybrid deployment is mixed environment with Skype for Business Online and On-Premises configuration. In Hybrid environment has existing on-premises deployment with users that were created in your on-premises Active Directory - with Skype for Business Online. Hybrid deployment allows you keep yours users on your Skype for Business or Lync Server on-premises and on Skype for Business Online using the Active Directory Synchronization to keep your on-premises and online users synchronized.