I find the current definition confusing:
What is a "lower-level part"? Take the domain name "en.wiktionary.org". To me, "lower-level part" mean "en" or "en.wiktionary". This is not what a subdomain is, at least not in the technical sense. In a techical sense, "wiktionary.org" is a subdomain of "org", "en.wiktionary.org" is a subdomain of "wiktionary.org", "bostonian.en.wiktionary.org" is a subdomain of "en.wiktionary.org", and so forth. (At least this is true from the IETF and Un*x technical perspective, Microsoft has a tendency to redefine words in a way that sows confusion.) From the technical side, you can only have a subdomain in the context of a specific domain name. There is no such thing as a "generic" subdomain, all subdomains are domains and so all go "all the way to the top". For that reason, I wrote the definition:
Now it may be that the teeming masses are using the word in some other sense, or maybe not given the example that was later added. There does seem to be some strange usage coming out of Wikipedia. So, should I add a definition for the technical sense, or what?
Now, there are also hostnames. Those can be either fully qualified hostnames, which are domain names and so end in a top-level domain, or unqualified hostnames that contain no periods. It might be that there's some sense of the word subdomain that's synonymous with unqualified hostname. --kop 05:47, 18 June 2006 (UTC)