(CNAME) A host's official name as opposed to an alias. The official name is the first hostname listed for its Internet address in the hostname database, /etc/hosts or the Network Information Service (NIS) map hosts.byaddr ("hosts" for short). A host with multiple network interfaces may have more than one Internet address, each with its own canonical name (and zero or more aliases).
You can find a host's canonical name using nslookup if you say
and then type a hostname.