A Top-Level Domain (TLD), also known as Domain Extension, refers to the last part of a Domain Name, located after the "dot" symbol. It mainly represents the purpose and type of the Domain. TLDs also identify something about the website associated with it, such as the organisation that owns it, or the geographical area where the website originates.
The Internet Corporation for Assigned Names and Numbers (ICANN), is the entity that manages most TLDs and operates the Internet Assigned Numbers Authority (IANA). Each TLD belongs to a separate Registry managed by a designated organisation still under the direction of ICANN.
Types of TLDs
TLDs are mainly classified into two categories: Generic TLDs and Country-specific TLDs.
Generic TLDs (gTLDs)
Generic Top-Level Domains (gTLDs) are TLDs that are not tied to any specific country and are "generic" in terms of being able to be used on the internet. If you are targeting a market globally, these Domain types best suit you. Examples are .COM, .ORG, .NET, .GOV, among others.
gTLDs also include industry-related Domains that can help create more awareness and interest in your business or brand. These types of Domains are more specific to their target market or which industry they belong to. For example, .PLUMBING for a plumber, and .cafe for a coffee shop.
Country-Code TLDs (ccTLDs)
Country-Code Top-Level Domains (ccTLDs) are TLDs that are assigned to countries based on a standard list of country-codes. Some countries have chosen to operate their ccTLD exclusively for Domains within their country or region. For example, .AU for Australia, .UK for United Kingdom, and .PH for the Philippines.
Note: Some TLDs do not allow registrations at the first level. An example of this is .AU, where it is currently not possible to register exampledomain.au only. Instead, you can register your Domain at what is called the second level. As to the case of .AU, you can register a .COM.AU, .NET.AU, or .ORG.AU, among others.