Domain registration

A domain name registry, is a 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 organisation 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. [1]
Domain names are managed under a hierarchy headed by the Internet Assigned Numbers Authority (IANA), which manages the top of the DNS tree by administrating the data in the root nameservers.
IANA also operates the .int registry for intergovernmental organisations, the .arpa zone for protocol administration purposes, and other critical zones such as root-servers.net.
IANA delegates all other domain name authority to other domain name registries such as VeriSign.
Some name registries are government departments (e.g., the registry for Sri Lanka nic.lk). Some are co-operatives of internet service providers (such as DENIC) or not-for profit companies (such as Nominet UK). Others operate as commercial organizations, such as the US registry (nic.us).
The allocated and assigned domain names are made available by registries by use of the WHOIS system and via their Domain name servers.
Some registries sell the names directly (like SWITCH in Switzerland) and others rely on separate entities to sell them. For example, names in the .com TLD are in some sense sold "wholesale" at a regulated price by VeriSign, and individual domain name registrar sell names "retail" to businesses and consumers.