A registrar is a company that has been authorized by ICANN to maintain the records of your approved domain name for the period of time you have paid for. To continue using your approved name you have to renew your name when the paid intervals are up. These records include the name, the contact information for the domain name administrator, billing contact, Support contact and others, the ip number that resolves your domain name with its associated name server and others.
When you purchaser a domain name it has an associated IP number that the name points to on the Registrars servers. These servers are known to the internet world as NAME SERVERS. If your registrar will also act as your hosting company then these numbers will remain unchanged and your website is located on their Name Servers.
There are companies that act only as registrars and companies that act solely as hosting companies and there are some that offer both services. It is very common to have your domain name registered with one company while another hosts your website. If you are in this category then the unique ip numbers that your registrar maintain must be pointed to the name servers of your hosting company.
Date : 7/3/2012