"TLD" and "TLDN" redirect here. For Temporary Location Directory Number, see Mobile Station Roaming Number. For other uses, see TLD (disambiguation). A top-level domain (TLD) is one of the domains at the highest level in the hierarchical Domain Name System of the Internet.[1] The top-level domain names are installed in the root zone of the name space. For all domains in lower levels, it is the last part of the domain name, that is, the last label of a fully qualified domain name. For example, in the domain name www.example.com, the top-level domain is com. Responsibility for management of most top-level domains is delegated to specific organizations by the Internet Corporation for Assigned Names and Numbers (ICANN), which operates the Internet Assigned Numbers Authority (IANA), and is in charge of maintaining the DNS root zone.
A top-level domain (TLD) is the last segment of the domain name. The TLD is the letters immediately following the final dot in an Internet address.
A 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.
In April 2009, ICANN proposed an expansion of the TLD system to allow anyone to register and reserve any unused letter sequence as a TLD for their exclusive use. A company that sold software, for example, might like to use .soft as a TLD. According to ICANN chief executive Paul Levins, such an expansion could lead to thousands of new TLDs in the next few years.
History
Originally, the top-level domain space was organized into three main groups: Countries, Categories, and Multiorganizations. An additional temporary group consisted of only the initial DNS domain, arpa and was intended for transitional purposes toward the stabilization of the domain name system.
Types of TLDs
IANA today distinguishes the following groups of top-level domains:
Descriptive top-level domains such as .guru
country-code top-level domains (ccTLD): Two-letter domains established for countries or territories. With some historical exceptions, the code for any territory is the same as its two-letter ISO 3166 code.
internationalized country code top-level domains (IDN ccTLD): ccTLDs in non-Latin character sets (e.g., Arabic or Chinese).
Test IDN TLDs were installed under test for testing purposes in the IDN development process.
generic top-level domains (gTLD): Top-level domains with three or more characters
unsponsored top-level domains: domains that operate directly under policies established by ICANN processes for the global Internet community.
sponsored top-level domains (sTLD): These domains are proposed and sponsored by private agencies or organizations that establish and enforce rules restricting the eligibility to use the TLD. Use is based on community theme concepts.
infrastructure top-level domain: This group consists of one domain, the Address and Routing Parameter Area (ARPA). It is managed by IANA on behalf of the Internet Engineering Task Force for various purposes specified in the Request for Comments publications.
Countries are designated in the Domain Name System by their two-letter ISO country code; there are exceptions, however (e.g., .uk). This group of domains is therefore commonly known as country-code top-level domains (ccTLD). Since 2009, countries with non–Latin-based scripts may apply for internationalized country code top-level domain names, which are displayed in end-user applications in their language-native script or alphabet, but use a Punycode-translated ASCII domain name in the Domain Name System.
Generic top-level domains (formerly Categories) initially consisted of gov, edu, com, mil, org, and net. More generic TLDs have been added, such as info.
The authoritative list of currently existing TLDs in the root zone is published at the IANA website at https://www.iana.org/domains/root/db/.
Internationalized country code TLDs
An internationalized country code top-level domain (IDN ccTLD) is a top-level domain with a specially encoded domain name that is displayed in an end user application, such as a web browser, in its language-native script or alphabet, such as the Arabic alphabet, or a non-alphabetic writing system, such as Chinese characters. IDN ccTLDs are an application of the internationalized domain name (IDN) system to top-level Internet domains assigned to countries, or independent geographic regions.
ICANN started to accept applications for IDN ccTLDs in November 2009,[6] and installed the first set into the Domain Names System in May 2010. The first set was a group of Arabic names for the countries of Egypt, Saudi Arabia, and the United Arab Emirates. By May 2010, 21 countries had submitted applications to ICANN, representing 11 scripts.
