Key Concepts and Features : Virtual domains
 
Virtual domains
A virtual domain (VDOM) is a complete FortiADC instance that runs on the FortiADC platform. The VDOM feature supports multitennant deployments. To do this, you create a virtual domain configuration object that contains all of the system and feature configuration options of a full FortiADC instance, and you provision an administrator account with privileges to access and manage only that VDOM.
For detailed information, see “Virtual Domains”.