The Name Servers of a domain name point out the DNS servers that deal with its DNS records. The IP of the web site (A record), the mail server that takes care of the e-mails for a domain name (MX records), any text record in free form (TXT record), pointing (CNAME record) and so on are obtained from the DNS servers of the website 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 want to open an Internet site, for instance, and you type in the URL, the web browser connects to a DNS server, which keeps the NS records for the domain address and the request is then pointed to the DNS servers of the webhosting provider where the A record of the site is obtained, so you can look at the content from the right location. Usually a domain address has two name servers that start with NS or DNS as a prefix and the distinction between the two is simply visual.