A domain name registrar is a company, such as allthe.domains, which facilitates the registration of a domain name and acts as an intermediary between the registry making the domain name available and the registrant who has chosen to register it. In some cases both registry and registrar can be the same, however, typically a registrar would be a commercial company. A registrar will be accredited with the registry and follow all its guidelines. 

Read more how registries, registrars, and registrants work together.