What is a Domain Registrar?
Domain names are managed through several regional registries, each of which is responsible for a generic three-letter domain (.com, .net, etc) or a "country code three letter domain" (.uk, .gs, .us, .fr, etc).
Each of the regional Registries are responsible for maintaining the top level of the domain name structure and management and ensures that it works with the Domain Name System. Most Registries delegate the ability to Register a new domain to independent Registrars. This is common with the generic three letter domains (gTLDs) and many of the country code three letter domains (ccTLDs). In these cases, each Registrar is required to maintain the correct information for the domain name and update the regional Registry accordingly.
See also All About Domain Registration