A TLD means Top-Level Domain. It identifies the most general part of the domain name in an Internet address. It is also the highest domain level in the hierarchical Domain Name System.
The TLD is the last part of the domain name, in other words, the last label of a fully qualified domain name. For example, in the fully-qualified domain name mydomain.com, the .com will be the TLD.
The Internet Corporation for Assigned Names and Numbers (ICANN) is responsible for managing most top-level domains and operating the Internet Assigned Numbers Authority (IANA). TLDs are also referred to as domain extensions.