What is a top-level domain?

A top-level domain (TLD) is at the top of the hierarchy of the Domain Name System (DNS) on the Internet. The top-level domain names are couched in the root portion of the name and they are not case-sensitive. Let’s consider this domain name: www.instance.com. Here, the top-level domain is com or COM.

The intricate job of managing most top-level domains is assigned to various organizations by the Internet Corporation for Assigned Names and Numbers (ICANN). This managing body also operates the Internet Assigned Numbers Authority (IANA) and is responsible for maintaining the DNS root zone.

At its inception, the top-level domain space was divided into three principal categories: Countries, Categories, and Multi-Organizations. Another temporary group existed, the ARPA or the Address and Routing Parameter Area. It comprised only the primary DNS domain and served all the transitional purposes that imparted stability to the domain name system.

As per the conventions of the Domain Name System, countries are denoted by their two-letter ISO country code. This group of domains is generally referred to as country-code top-level domains (ccTLD).

The Categories group consists of the generic top-level domains. This group once consisted of COM, GOV, EDU, ORG, NET, and MIL.

As the processes on the Internet evolved and grew more complex, it became imperative that other generic top-level domains were created. The functionalities for some domains conceived initially were also generalized, altered, or designated to special organizations to ensure that they were maintained while remaining true to their purpose.

Today, after all these modifications, the IANA has come to recognize the following groups of top-level domains:

  1. Country-code top-level domains (ccTLD): These are domains with two letters in their names. They were established to represent countries or territories or their international domain names (IDN ccTLD). Barring a few cases, the code for any territory is identical to its two-letter ISO 3166 code.
  2. Generic top-level domains (gTLD): These are top-level domains that have three or more characters in their names.
  3. Unsponsored top-level domains: These domains conform to the policies established by ICANN. These policies, in turn, are followed by the Internet community all over the world.
  4. Sponsored top-level domains (sTLD): The functioning of these domains were conceived and then funded by private agencies or organizations. These organizations formulate and execute the rules that govern the eligibility criteria to use the TLD. The usage is determined by community themed subjects.
  5. Infrastructure top-level domain: This group currently has only one domain, the ARPA. It is supervised by IANA on behalf of the Internet Engineering Task Force and carries out the various functions listed in the Request for Comments.

A comprehensive list of the prevalent TLDs in the root zone is available on the IANA website.

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