NT domain: A collection of computers in a network that shares a common database and security policy.
Web domain: The highest-level name in a network address (URL) that signifies who owns the address (e.g., www.microsoft.com); every Web page that you can access through a specific URL.
Web site: Any addressable location that contains HTML content; a collection of one or more Web pages; FrontPage uses the term Web to refer to Web sites.
Sub-Web: A FrontPage term for child Web sites that have FrontPage Server Extensions installed on them; sub-Webs exist under a root Web (the highest level of the Web domain) or, in the case of FrontPage 2000, under other sub-Webs and can have their own authors, themes, and administrators.
Web (HTTP) server: A computer that uses HTTP to serve Web content (HTML documents and associated files) for a given Web domain; computers today can run a Web server for each Web domain.
Virtual server: A copy of the server executable and its attendant libraries running in memory on the server machine; on a Web server machine capable of hosting multiple Web domains, each domain runs on its own virtual server (i.e., a virtual server exists for each Web domain residing on one Web server).
Application server: With respect to the Internet, a server that runs and manages Web applications in a given Web domain (e.g., you could consider IIS an application server because it manages and serves Web-based applications).