The Name Servers of a domain name reveal the DNS servers that are responsible for its DNS records. The IP address of the web site (A record), the mail server that takes care of the emails for a domain (MX records), any text record in free form (TXT record), pointing (CNAME record) and so on are extracted from the DNS servers of the web hosting provider and for any domain name to be using them and to be directed to their hosting platform, it ought to have their name servers, or NS records. If you wish to open a website, for instance, and you type in the URL, the web browser connects to a DNS server, which keeps the NS records for the domain and the request is then redirected to the DNS servers of the webhosting provider where the A record of the web site is obtained, so that you can see the content from the proper location. Usually a domain name has 2 name servers that start with NS or DNS as a prefix and the difference between the two is only visual.