TLD identifies something about the website associated with it, such as its purpose, the organization that owns it or the geographical area where it originates. Each TLD has a separate registry managed by a designated organization under the direction of the Internet Corporation for Assigned Names and Numbers (ICANN).
In our Internet address,http://whatis.techtarget.com: com is the top-level domain name;techtarget.com is the second-level domain name; and whatis is a subdomain name. All together, these constitute a fully-qualified domain name (FQDN); the addition of HTTP:// makes an FQDN a complete URL.
ICANN identifies the following categories of TLDs:
- Country-code top-level domains (ccTLD) -- Each ccTLD identifies a particular country and is two letters long. The ccTLD for the United States, for example, is .us
- Infrastructure top-level domain -- There is only one TLD in this group, ARPA (Address and Routing Parameter Area). The Internet Assigned Numbers Authority (IANA) manages this TLD for the IETF.
- Sponsored top-level domains (sTLD): These are overseen by private organizations.
- Generic top-level domains (gTLD) -- These are the most common and familiar TLDs. Examples include "com" for "commercial" and "edu" for "educational." Most gTLDs are open for registration by anyone, but there is also a subgroup that is more strictly controlled.