This address is different from the other addresses in that it is not designed to be used in the normal firewall policy configuration. It is intented to be used only with explicit web proxies, and then only as a desination. In some respects it is like a FQDN address in that it uses DNS to look up the IP address that represents but it then goes a little more granular and further filters by the url that is used to specify a location within the website itself. Wildcard characters can even be used to keep the address from being too granular.