After some research, I think I understand the distinction that
techno-purists want to make between "hosts" and "subdomains". Domains
and subdomains will have name server (NS) records and NO host records
in the "zone" file pertaining to the parent domain, while "hosts" will
have one or more host records (A, CHAME, MX, etc.) and NO name server
(NS) records for that host in the domain's zone file.
Unfortunately, I had to wade through mounds of inane anecdotes and
confusing geek-speak of techno-purists trying to explain the
difference - none of whom would actually explain how to create a
subdomain (add "NS" records to a domain's zone file).
The problem still remains that most DNS providers (GODADDY, Network
Solutions, and dozens of others) don't agree with the previous
distinction, and they provide browser user interfaces for setting up
"subdomains" by adding "host" records to the domain's zone file.