Difference between a Virtual Server, Sub-Server, and Virtual Host

Hello i understand your question. ;)

i'm no native english so to hard for me to explain. Little try but please asked for more and someone else if not right or understand!

"Virtual" is the term how virtualmin is using talking about.

They don't like domains. / urls uh URI.. ;) i trie to explain with that... hihi

The Host should be the domainname hostname used for the Box where Virtualmin is running on.

A server / virtual server is kind of domain with all the possibility's for that. ( so urlname.tld kind of).

Sub-server is with real directory's / diskspace (a alias fore example doesn't) for a virtual server, so sort off subdomain if you understand that better ( not 100% right term) so subdomainname.urlname.tld

Now it comes the problem with that that www.urlname.tld is should be called subdomain to! therefore you shouldn't have / use www.sub-server / so as i explain www.subdomainname.urlname.tld

Using as whatevername.main-urlname.tld is common for mail., ftp. and so on. virtualmin is using autoconfig. what gives problems with some dns hosters not allowing that! Also using autodiscover. and m.

You can test After configured and resolving on the web ( that takes some time) with external dns test tools and sites as mxtoolbox and so on that these DNS settings for all those are correct

With the SNI "technic" it is possible to have al those running with SSL cert on one IPv4 even one IPv6 but IPv6 adresses are free till.... endless for the time beeing so using more IPv6 is my advice, and while IPv4 costs some you could use one IPv4 and SNI technics having more Virtual-server and sub servers on one IP though using SSL working ok. ( so most user use a virtualmin BOX nowadays with SNI and also common for SSL cert the free letsencrypt)

eh read also some here https://www.virtualmin.com/comment/785611#comment-785611