Generic Top-Level Domains or gTLDs are likely the most familiar to people. These are the domains that end in three-letter domains like .com, .net, and .gov.
First let’s describe a TLD or Top-Level Domain. A domain name is a hierarchical name in the domain name system (DNS) given to a destination usually reachable over the public internet, though domain names are also used in private networks. Domains are hierarchical, and the top-level domain is just that, the highest level of that domain. Top-Level domains are maintained by IANA, the Internet Assigned Numbers Authority, which is a part of ICANN, the Internet Corporation for Assigned Names and Numbers.
Originally there were only a few TLDs. These were:
Organizations, non-profit usually
Many of the original uses are no longer restricted by IANA, so you may now find companies using both .com and .net for example. However, domain.com and domain.net are two totally different domain names and will take you to different sites, unless a company has somehow redirected these to the same destination. There are now many more gTLDs which are supported by IANA, over 1500 as of March of 2021.
A sponsored TLD generally has an individual or a group who are sponsoring a specialized gTLD. Whereas a non-sponsored gTLD is used for unrestricted purposes.
Sponsored TLDs may represent groups of a certain ethnicity, geography, or even career.
Examples of sponsored TLDs are:
Société Internationale de Télécommunications Aéronautiques
General Services Administration
Museum Domain Management Association
Universal Postal Union
Non-sponsored gTLDs are monitored and managed centrally by ICANN as mentioned above. These include the more common TLDs mentioned above such as .com and .net.
Generic TLDs can be either sponsored or non-sponsored as discussed above. Another kind of specialized TLD which represents a country. Most countries will have their own ccTLD. Recently a new kind of ccTLD has also been created which is an Internationalized TLD. These include native language characters.
Examples of ccTLDs:
As mentioned there are now over 1500 gTLDs. Though this is subject to change, the most used as of 2021 are: