The following terms are used in discussing domains:
Authcode—A secret pass phrase that shows verifiable proof of ownership of a domain.
ccTLD (Country Code Top Level Domain)—ccTLDs are country code top-level domains. Examples of ccTLDs are .CA (Canada), .US (United States), and .UK (United Kingdom). Every country, and some territories in the world have a reserved, two letter country code domain that is theirs to use as they see fit. Some countries run their own ccTLD registry, others outsource it to a private company, and still others sell rights to their ccTLD to third parties to run as they see fit. For example, .TO is used more by Torontonians than Tongans and .TV has more American television content than members of the native Tuvalu culture.
DNS—Domain Nameserver. Maps and translates domain names (eg. Tucows.com) to the IP address (eg. 126.96.36.1991). For more on DNS terms, take a look at What is DNS?
Domain Registrant—A Registrant is the person or company who registers a domain name. For example, Jessica Smith (Registrant) registers the name jessicasmith.com.
Domain Registrar—A Registrar (or Domain Name Registrar) is an organization like Tucows that has control over the granting of domains within certain TLDs (top level domains, like the generic .COM/.ORG/.NET or country-specific .CA/.US/.MX and so on).
Domain Registry—The Registry is the system backend that is maintained by the operators of the TLD. Registrars write new names to a central registry database, from which the authoritative root (essentially, a table of all domain names) is built. For example, Verisign Global runs the registry for .COM, .NET and .ORG, Neustar runs the .BIZ registry, and Afilias runs the .INFO registry to which qualified registrars have shared access. In the case of many ccTLDs, the registry and registrar functions are combined within one entity.
gTLD (Generic Top Level Doman)—gTLDs are generic top-level domains that are not associated with any country, such as, .COM, NET, .ORG, .INFO, .BIZ, .NAME, MOBI, .TEL, and .ASIA
ICANN—Internet Corporation for Assigned Names and Numbers. Manages assignment of domain names and IP addresses; defines policies.