Service Host is a Vizrt component that abstracts the Windows Service layer. The Service Host operates with plug-ins that implement a desired service or functionality. The Service Host itself takes care of logging and all the Windows Service stuff.
An example is the Control Mode plug-in, which by default is registered as a Windows service called ServiceHost.control. Control Mode provides a REST interface and comes with a web-based user interface. It provides the necessary functionality to manage the Service Host plug-ins and installed Viz Engine instances.