Meaning of a Domain Name Extension


"Domain name extension" is a common term for what is technically called the "top-level domain," or TLD, of a website. The TLD is whatever comes after the final "dot." For the website, for example, the domain name extension is ".com." The TLD is akin to the area code in a phone number or the ZIP code in a postal address: It's where your computer starts its search for a website.


  • There are two basic types of domain name extensions: country code top-level domains, and generic top-level domains. Further, generic top-level domains can be either sponsored or unsponsored.

Country Codes

  • If the domain name extension of a website is only two characters long, then it's a country code top-level domain, or "ccTLD." Examples include ".us" for the United States, ".br" for Brazil and ".de" for Germany (Deutschland). Country codes are managed by the Internet Assigned Numbers Authority, and as of 2010, there were nearly 250 ccTLDs, one for every country in the world plus special-status territories such as Hong Kong (.hk), the Falkland Islands (.fk) or Puerto Rico (.pr). Each country designates a government agency or a private company to handle registrations under its ccTLD, and each can set its own rules for who or what can register. Some allow only their own citizens or businesses to register, others allow anyone to register--and some actively market their ccTLDs as a source of revenue. Two examples of the latter are the Pacific Ocean island nations of Tuvalu (.tv) and the Federated States of Micronesia (.fm).


  • The most common domain name extensions are the unsponsored generic TLDs. They're called "unsponsored" because no agency approves registrations; anyone anywhere in the world can register domains with these extensions. Unsponsored TLDs include ".com," ".org" and ".net." Generally, ".com" sites are commercial, ".org" websites belong to non-profits and trade associations, and ".net" addresses are used by Internet-related companies, but these categories are not enforced at all. If you go to register a domain with a ".org" extension, no one is going to check whether your organization qualifies. Other unsponsored generic TLDs include ".info," ".biz" and ".name."


  • Sponsored generic top-level domains are those that have a gatekeeper--an agency or organization that decides who can and can't register. The most familiar sponsored extensions are ".gov," which is managed by the U.S. federal government; ".edu," which is open only to post-secondary educational institutions accredited by an agency recognized by the U.S. Department of Education; and ".mil," reserved for the U.S. military. Other sponsored TLDs include ".aero" for the air-transport industry; ".asia" for Asia-Pacific entities; ".cat" for Catalan language and cultural sites; ".coop" for cooperatives; ".int" for international organizations; ".jobs" for human resources managers; ".mobi" for the mobile communications industry; ".museum" for museums; and ".travel" for the travel and tourism industry.


  • Lists of all websites registered under each TLD are stored on "root servers" maintained in 13 clusters around the world for redundancy. When you punch a Web address into your browser, the first place it looks is the root server list for the TLD in the address; that list points it to the proper "name server" for the website.

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