A domain name or domain is, like www.example.com which is connected to a specific IP Loosely speaking, it's the address of your website. 

All domains have at least two Name  servers   such as NS1.EXAMPLE.COM and NS2.EXAMPLE.COM

When you use an alphanumeric address such as WWW.EXAMPLE.COM, your computer needs to understand what numerical IP addresses it needs to contact, and this is accomplished through DNS servers.
and your request for anything related to the domain name gets sent to one of these servers.  In response, the DNS server sends back the IP address that you should contact.  This works for the Website, Mail Servers, and anything else based on the domain name.

 For example, the machine at Domain India  with the IP address http://192.18×.18×.206   can also be referred to as: www.domainindia.org


So what is Domain Name Servers 

Domain Name Servers (DNS) are the Internet's equivalent of a phone book. They maintain a directory of domain names and translate them to Internet Protocol (IP) addresses.

This is necessary because, although domain names are easy for people to remember, computers or machines, access websites based on IP addresses. 

Information from all the domain name servers across the Internet are gathered together and housed at the Central Registry. Host companies and Internet Service Providers interact with the Central Registry on a regular schedule to get updated DNS information.