Subdomain: "A domain is a subdomain of another domain if it is

contained within that domain. This relationship can be tested by

seeing if the subdomain's name ends with the containing domain's

name." (Quoted from [RFC1034], Section 3.1). For example, in the

host name "nnn.mmm.example.com", both "mmm.example.com" and

"nnn.mmm.example.com" are subdomains of "example.com".