The Top-level domain (TLD) refers to the last segment of a Fully Qualified Domain Name, or the part that follows immediately after the “dot” symbol. The TLD specifies the domain at the highest level in the tree hierarchy of the Domain Name System and is required for a domain name to be “Fully Qualified”. You cannot visit a website on the internet using a domain name without knowing its TLD.
For example, in the domain name www.domain.com, the top-level domain is “.com.”
Initially TLDs were mainly classified into two categories: Generic TLD’s and Country Specific TLD’s. However, as the internet grew, several different TLD categories were introduced and there are now thousands of different TLD’s.
For the most part, the general population will know their country’s specific TLD (Mine is “.com.au”), they will most likely know the generic TLD “.com” and possibly “.UK” if they are Europe based.., as well as a few of the commonly used generic ones. The first set of TLD’s were all generic and included:
.com, .org., .net., .edu, .gov & .mil
In 1985 & 86 the first Country Code Top Level Domains were introduced, some of them included:
.us, .uk., .il, .au, .de .fr .jp
The introduction of Country Specific TLDs was quickly adopted and widely used by those who had access to them. The U.S however decided to adopt .com as their predominate TLD over .us. By 2000, any country could use their 2 letter ISO code as their Country Code TLD and by 2010 the use of non-Latin alphabet was also introduced. This is known as Internationalized ccTLD.
With the rise of the internet, the demand for domain names obviously grew to. And with that, as well did the desire for unique Top level domain names. By the 2000s, the Internet Corporation for Assigned Names and Numbers (ICANN) was established to overlook the IANA (IP Address allocation) and maintain the DNS root zone (issuance of TLD’s). In the early 2000’s, ICANN had a very strict policy on what TLD’s can be used for fully qualified domain names, and generally unless it was a country specific or one of the few generic TLDS, it would not allowed with only very few exceptions.
From the 80’s up until 2011, there had been only 16 additional generic TLD’s added to the original 6, however in 2011 ICANN’s board voted to end most restrictions on the creation of generic top-level domain names, where at the time there was currently only 22. Companies could then apply for their own gTLD.
Fast forward 6 years and there are now thousands of different top level domains. As of 2105, the IANA categorizes Top Level Domains into the following groups.
Generic Top Level Domain (gTLD): These are now classified as top level domains with three or more characters.
Restricted Generic Top Level Domains (grTLD): These are generic TLD’s that are reserved for a particular use. For example .gov is for the U.S government and .edu is for the department of education.
Country Code Top Level Domain (ccTLD): These are two letter TLD’s that represent specific countries or regions go by the two letter ISO code of that country/region.
Internationalized country code top level domains (IDN ccTLD): These are country code TLD’s that use letters other than Latin. For example, Chinese, Arrabic, Hebrew.
Sponsored Top Level Domain (sTLD): Is a specialized top level domain that has been sponsored by a certain organization or agency that represents the specific community that is most affected and involved with the TLD.
These domains are proposed and sponsored by private agencies or organizations that establish and enforce rules restricting the eligibility to use the TLD. For example, the .travel is sponsored by Tralliance Corporation, which limits the registration of the .travel TLD to those in the travel industry.
There is also “Infrastructure Top Level Domain (iTLD)” & “Test Top Level Domains (tTLD)”
