A top level domain (TLD) is, in the domain name system (DNS), the highest level of the hierarchy after the root servers.
DNS is the network of programs and databases that cooperates to translate domain names to IP addresses. Domain names are user-friendly (i.e., easy to remember) substitutes for IP addresses, which are unique numeric identifiers that are used for addressing on the Internet and other TCP/IP (transmission control protocol/Internet protocol) networks.
In a domain name, the TLD is the last part of the name, that is, the segment after the final dot and furthest to the right. For example, it is the org in bellevuelinux.org.
TLDs are classified into two main groups: generic (gTLD) and country codes (ccTLD). The former, which are the most frequently used, each consist of at least three alphabetic characters. They include names such as .com (commercial), .net (network), .org (organization), .gov (government), .edu (education) and .mil (military). Most gTLDs are available for use worldwide, but for historical reasons .gov and .mil are restricted to the U.S. government and U.S. military. The number is occasionally increased.
The great bulk of TLDs are country codes. These consist of two letters that represent individual countries. Examples include .au (Australia), .br (Brazil), .ca (Canada), .cn (China), .fr (France) .ie (Ireland), .it (Italy), .jp (Japan), .th (Thailand). .uk (United Kingdom), .us (United States) and .za (South Africa).
Second level domain names are what are registered on behalf of organizations and individuals in a TLD registry. For example, it is the bellevuelinux in bellevuelinux.org.
Created October 25, 2005.