The Domain Name System (DNS) has a tree structure or hierarchy, with each node on the tree being a domain name. A subdomain is a domain that is part of a larger domain, the only domain that isn't also a subdomain is the root domain. For example, "mail.example.com" and "calendar.example.com" are subdomains of the "example.com" domain, which in turn is a subdomain of the "com" top-level domain (TLD).

A "subdomain" expresses relative dependence, not absolute dependence: for example, wikipedia.org comprises a subdomain of the org domain, and en.wikipedia.org comprises a subdomain of the domain wikipedia.org. In theory, this subdivision can go down to 127 levels deep, and each DNS label can contain up to 63 characters, as long as the whole domain name does not exceed a total length of 255 characters. But in practice some domain registries have shorter limits than that.

Uses

Subdomains are commonly used by organizations that wish to assign a unique name to a particular department, function, or service related to the organization. For example, a university might assign "cs" to the computer science department, such that a number of hosts could be used inside that subdomain, such as mail.cs.example.edu or www.cs.example.edu.

Vanity Domain

Main article: Vanity domain

A subdomain is sometimes termed a vanity domain, can be a subdomain of an ISP's own domain aliased to an individual user account or expresses the individuality of the person on whose behalf it is registered.

From Wikipedia under the GNU Free Documentation License
Mon Jul 6 12:35:15 2009

Does anybody know whre I can get a free web host with a free subdomain & includes free CGI usage?
Q. I'm planning to create a new website in the future(within the next year) and I don't want to use a credit card but I need CGI scripting. So any ideas?
Asked by andrewland665 - Sat Sep 15 01:14:45 2007 - - 2 Answers - 0 Comments

A. If you are serious about websites either for personal or your business, don't go to free web hosting as they are usually not reliable and you may end up losing all your hard work. Free web hosts usually put advertisements on your websites and it could be annoying. If you like to create websites (usually you will end up more than 1 website, I got more than 100 websites in about 6 months' time), go for multiple web hosting services where you could host all your websites in one account. I would like to suggest following webhosting which I use, they are excellent. Hostmonster They offer hosting of "unlimited domains" and you will get massive webspace of 3000 MB (300 GB ). They only charge $5.95/month and they offer "a free Domain Name"… [cont.]
Answered by soekind - Sat Sep 15 08:33:41 2007

How do you change the A Name of a subdomain in CPanel?
Q. I need to point a subdomain to an IP address not a folder on my site any help? Im on a hosting provider also, i forgot to add that to the main part :P. I have a domain name registered elsewhere. I pointed it to the DNS servers of my host and it works fine. I just wanted to know if i can make a subdomain point to an IP address.
Asked by Hc2995 - Thu Apr 16 18:37:05 2009 - - 1 Answers - 0 Comments

A. Assumption 1: You have your own DNS server assumption 2: You have cPanel DNS installed on that DNS server assumption 3: You have registered your DNS server as the authoritative source for your domain. If any of those assumptions are false, the answer is you can't. 1) Click on DNS Editor in the cPanel Home Page 2) Go down to the new entries section at the bottom 3) Enter in your subdomain under Domain 4) Set a good TTL. 7200 should be good 5) Set the record type to 'A' 6) Enter the IP address to the box that appears to the right of the 'A' 7) Save changes 8) Wait for propigation
Answered by M. L. - Thu Apr 16 18:48:46 2009

How does a subdomain work?
Q. okay - say I have myphotos.com I want another website - that is different -- if i make a sub domain like peoplepictures.myphotos.c om is it possible to type in peoplepictures.com and get to that site? I don't know if that is understandable - I want to make another website without having to go through hosting a new site - but I also want to make cards with peoplepictures.com - even if it does go to peoplepictures.myphotos.c om - i still want people to beable to type in the other address -- would a subdomain work in that way? thanks!!
Asked by doubt133 - Wed Mar 14 03:30:27 2007 - - 2 Answers - 0 Comments

A. A sub domain may not work that way. infect what you are thinking of the sub domain is exactly another domain on the same package. A sub domain shall always follow the domain name, and not stand alone. If your host provide you with multi domain hosting, you should go for another dmain on the same space.
Answered by farcity79 - Wed Mar 14 03:49:57 2007

From Yahoo Answer Search: "Subdomain"
Fri Jun 12 09:31:42 2009

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A Twitter account username is a tertiary-level domain, and would function in social search much like a secondary-level Web site domain or tertiary subdomain ...
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The new subdomain resource allows clientele to design custom embroidery and order selected items directly from EmbroidMe. The new process eliminates the ...
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Ecommerce Know-How: Mobile Commerce in Four Steps

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... website and domain to be more mobile-friendly using a handset-specific cascading style sheet (CSS) and, if you must, a mobile specific subdomain . ...

From Google News Search: "Subdomain"
Fri Jul 10 12:15:01 2009

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[source page]

If you chose to go the web user route then for the subdomain dan binasys co uk and the web user dan we would do the following

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[source page]

Anda dapat langsung mengakses subdomain pada addon domain Anda Catatan Subdomain akan membuat direktori baru pada domain utama sesuai dengan nama subdomain yang dibuat

From Yahoo Image Search: "Subdomain"
Wed Jul 8 09:58:34 2009

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Sat, 27 Jun 2009 14:14:53 GM

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From Google Blog Search: "Subdomain"
Sun Jun 28 12:19:34 2009