A top-level domain (TLD), sometimes referred to as a top-level domain name (TLDN), is the last part of an Internet domain name; that is, the letters which follow the final dot of any domain name. For example, in the domain name www.example.com , the top-level domain is com (or COM , as domain names are not case-sensitive).
The Internet Assigned Numbers Authority (IANA) currently classifies top-level domains into three types:
- country code top-level domains (ccTLD): Used by a country or a dependent territory. It is two letters long, for example .us for the United States.
- generic top-level domains (gTLD): Used (at least in theory) by a particular class of organizations (for example, .com for commercial organizations). It is three or more letters long. Most gTLDs are available for use worldwide, but for historical reasons .mil (military) and .gov (governmental) are restricted to use by the respective U.S. authorities. gTLDs are subclassified into sponsored top-level domains (sTLD), e.g. .aero, .coop and .museum, and unsponsored top-level domains (uTLD), e.g. .biz, .info, and .name.
- infrastructure top-level domains (iTLD): The top-level domain .arpa is the only confirmed one. .root has been known to exist without reason.
A full list of currently existing TLDs can be found at the list of Internet top-level domains.
