"Virtual host" here has no relationship to virtualization systems like VMWare, Xen or Hyper-V. When talking about Apache, these represent multiple websites on the same machine, possibly even on the same IP address.
When you have multiple VSys Live sites on the same machine, Apache - the web server that is the part of VSys Live that faces the world - needs to know which site to show when a request comes in from a browser. IP-based virtual hosts use the IP address of the connection to determine the correct VSys Live site to show. Therefore you need to have a separate IP address for each site. With name-based virtual hosting, the server relies on the browser to report the hostname as part of the HTTP headers. Using this technique, many different hosts can share the same IP address.
When a request arrives, Apache will look at each installed VSys Live site and try to find one where the Server name or Server alias matches the requested hostname. If it finds one, then it uses that VSys Live site. If no match is found, then the first VSys Live site (lowest Order) will be used.
This is where the installation settings for each of your VSys Live sites come into play.