The Name Servers of a domain reveal the DNS servers that are responsible for its DNS records. The Internet protocol address of the website (A record), the mail server that takes care of the emails for a domain address (MX records), any text record in free form (TXT record), directing (CNAME record) and so on are obtained 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 has to have their name servers, or NS records. If you would like to open a site, for instance, and you enter the URL, the web browser connects to a DNS server, which keeps the NS records for the domain and the request is then forwarded to the DNS servers of the hosting company where the A record of the web site is obtained, enabling you to see the content from the correct location. Normally a domain address has a couple of name servers that start with NS or DNS as a prefix and the difference between the two is just visual.