CNAME Canonical Name

A second name for the same address. www.example.com as a CNAME onto example.com means: keep asking over there. The address bar in the browser does not change, so it is not a redirect.

A CNAME does not get along with other records of the same name. That is why it never sits on the domain itself, only on sub-addresses like www or autodiscover.

If a CNAME points at a target that no longer exists, somebody else can take that target over and put content out under your address.