Nathan called it a sub-domain (and you agreed)...
It's not a sub-domain it's a host. Only hosts can have IP addresses.
Charles, you appear to be talking about setting up "A" records (aka DNS
host records) which I would call mapping sub-domain names to IP addresses.
For a definition of sub-domains see:
I began learning about sub-domain names after having to pay what appeared
to me to be an outrageous premium for a wildcard certificate for *.
my-domain.com, where the asterisk refers to "all" sub-domains of a