Create sub sub domains, URL with two subdomains

Question

If i have a site with url www.example.com, is possible to have another subdomain with the subdomain www? for example www.extra.example.com. I don't sure about this.

I tried to find some information, but i don't have enough experience in that area

Answer 1

qux.bar.foo.example.com

com is the top-level domain,
example is the second-level domain,
foo is the third-level domain,
bar is the fourth-level domain,
qux is the fifth-level domain.

And yes, you can have more levels (DNS calls them "labels").

Many people mean only the third-level domain when they say "subdomain" (or fourth-level domain in case of an effective top-level domain like co.uk), probably because most domains don’t have more levels, however:

foo is the subdomain of example.com,
bar is the subdomain of foo.example.com,
qux is the subdomain of bar.foo.example.com.

By the way, www is no special label, just a convention.

Answer 2

Yes it is. In your example, the two sub-domains "www" and "www.extra" are different.