Windows SharePoint Services - Virtual Servers or Web Applications ?

The WSS product team initially used the term virtual server to describe an IIS Web site that had been extended with WSS functionality. The current WSS version and supporting documentation use the term Web Application mainly to avoid confusion with another Microsoft product of the same name. Unfortunately we must remember that the new term Web application and the old term virtual server are often both used interchangeably.

For example, the WSS object model provides the (now obsolete) SPVirtualServer class to program against Web application objects.