The Name Servers of a domain reveal the DNS servers that are responsible for its DNS records. The IP of the website (A record), the mail server that takes care of the e-mails for a domain (MX records), any text record in free form (TXT record), directing (CNAME record) etc are taken from the DNS servers of the web hosting provider and for any domain address to be using them and to be pointed to their hosting platform, it needs to have their name servers, or NS records. If you want to open an Internet site, for example, and you enter the URL, the web browser connects to a DNS server, which keeps the NS records for the domain address and the request is then forwarded to the DNS servers of the webhosting provider where the A record of the web site is retrieved, so that you can see the content from the correct location. Commonly a domain name has two name servers that start with NS or DNS as a prefix and the difference between the two is simply visual.