A domain name registrar is a company accredited by the Internet Corporation for Assigned Names and Numbers (ICANN) and/or by a national ccTLD authority to register Internet domain names. These "retail" companies are often distinct from the "wholesale" domain name registry operator.
ICANN has authority over gTLDs, or Generic Top Level Domains. Examples of gTLDs include .com, .net, .org and .mobi. ICANN does not have authority over ccTLDs, or Country Code Top-Level Domains, though it is quite common for domain name registrars to offer ccTLD registration services as well. Many registrars provide DNS hosting service, but this is not required, and is often considered a separate service.
An individual or end-user alone cannot register and manage their domain name information with ICANN. A designated registrar must be chosen to have one's domain names registered and managed with ICANN on their behalf.
Only one designated registrar may modify or delete information about a domain name. The competition that SRS created enables the end user to choose from many registrars offering different services at varying prices. It is not unusual for an end user to wish to switch registrars. Thus, there is the domain name transfer clause.