TLD - Top-level domain is a domain at highest level of Domain Name System (DNS) such as .com, .net, etc. Management of most TLDs is by Internet Corporation for Assigned Names and Numbers (ICANN), which operates Internet Assigned Numbers Authority (IANA).
List of TLDs
ccTLD - country code top-level domain is an Internet top-level domain generally used or reserved for a country, a sovereign state, or a dependent territory. In 2010, IANA) began implementing internationalized country code TLDs.
Registry - database of all domain names registered in a top-level domain. A registry operator, also called a Network Information Center (NIC), is the part of the Domain Name System (DNS) of the Internet that keeps the database of domain names, and generates the zone files which convert domain names to IP addresses. Each NIC is an organization that manages the registration of Domain names within the top-level domains for which it is responsible, controls the policies of domain name allocation, and technically operates its top-level domain. It is potentially distinct from a domain name registrar.
Registrar - an organization or commercial entity, such as GoDaddy, accredited by a generic top-level domain registry (gTLD) and/or by a country code top-level domain (ccTLD) registry, to manage the reservation of Internet domain names in accordance with the guidelines of the designated domain name registries and offer such services to the public.
Accredited list of Registrars
See Wikipedia for more info.