I am talking about the "www" which is the acronym of "world wide web", and it's automatically assigned to any domain name, so usually domain.com and www.domain.com points to the same host, unles if the sysadmin changes it which rarely happens.
I am talking about the "www." and NOT any other subdomain that the sysadmin/webmaster can add/change or remove.
I am sorry if you misunderstand what I am talking about.
Thank you so much for your explanation, I really appreciate it.