What is a Top-Level Domain (TLD)?

A top-level domain is the suffix that is attached to the end of a Domain Name. .com, .net and .org are Top-Level Domains in the hierarchical Domain Name system. In the Domain Name ‘cpwebhosting.net‘, the .net is the Top-Level Domain. Top-Level Domains are the highest-level category of Internet names.

What is a Registry?

A registry is a company or organization that maintains a centralized registry database for the Top-Level Domains. Currently there is only one Registry for every Top-Level domain, .com, .net and .org. NSI Registry maintains this Registry.

thanks tcheck, I have one more question,What is a Registrar?

A registrar is an ICANN accredited company or organization that is authorized to provide registration services for the top-level domains such as .com, .org and .net. Registrars have contractual agreements with their customers.

A Registrar submits all newly registered domains into the Registry.