Definition of a Subdomain Name
To help organize the Internet and make it easy to use, the Internet Corporation for Assigned Names and Numbers (ICANN), the governing organization for domain-naming conventions, put forth the idea of a domain name system (DNS), a tree-type structure for website files that reside in a certain domain, or URL, of a webpage. Sub-domains are files contained within a domain, in a lower level, that group files by type or that point to specific servers.
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Domain Names
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Domain names are the unique names of websites, such as "google.com" or "yahoo.com." The Internet Protocol (IP) address does the true work behind the scenes, calling up a server, computer or website when you enter its address, or URL. Most IP addresses are long strings of numbers or letters that are hard to remember. In essence, a domain name points to an IP address so you don't have to remember all those numbers.
Hierarchy
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Domain names are organized into a hierarchy of files. This hierarchy, better known as DNS, adheres to certain rules put forth by ICANN. The top-level domain name is the basic domain name, such as "google.com" or "yahoo.com." Using the DNS hierarchy, you can organize the files on a domain by placing them in directories at the top level, secondary level or in a sub-domain.
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Sub-Domain Names
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Sub-domains represent a level of files that exist within a domain and use that domain as a URL suffix. The names within the URL are separated by dots "." in descending order from the top-level domain. For example, if your top-level domain's URL was sampledomain.com, sub-domains within it might be email.sampledomain.com, photos.sampledomain.com or specificimages.photos.sampledomain.com.
Sub-Domain Naming Conventions
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ICANN has limited the length and number of sub-domain names. A sub-domain label must be 63 or fewer characters with fewer than 127 sub-domains per top-level domain. The total of all characters in all sub-domain names within a domain must be 255 or fewer.
Uisng Sub-Domains
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Sub-domains are used in a variety of situations. Sub-domains can be used to organize files in a domain by type or use, such as images; to represent content that exists on different servers or to point to different servers entirely; and to differentiate between webpages and Web servers -- for example, those that send email.
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References
- Photo Credit Photos.com/PhotoObjects.net/Getty Images
