edit Top-Level Domain (TLD)
A top level domain is the part of a website name that comes after the dot - here are a few examples and there are dozens more:
Top-Level Domains is essentially another name for the types of URLs that allow us to navigate the internet. The domain name system (DNS) is a way for users to get around the internet without having to use unique numeric identifiers (IP addresses) that are hard to remember. DNS strings are user generated text that represents these numbers. For example "www.icann.org" is a much easier to remember and type accurately than "220.127.116.11", although both represent the internet URL we'd call "icann.org".
ccTLDs -- are a subset of Top-Level Domains that are reserved for countries or a dependent territory. For example, .ca in Canada, .uk in the United Kingdom, .br in Brazil, etc. See the complete list of ccTLDs at Iana.org.
gTLDs -- Generic Top-Level Domains are everything else. These indicate the type of organization they are in use for, for example: ".museum" is in use for museums, ".gov" for governments and their agencies in the US; however others have more recently had their restrictions lifted, so that while generally ".org" was for organizations. See the complete list of gTLDs at Iana.org.