The Name Servers of a domain point out the DNS servers that handle its DNS records. The IP of the site (A record), the mail server that deals with the emails for a domain name (MX records), any text record in free form (TXT record), pointing (CNAME record) and so forth are extracted from the DNS servers of the website hosting company and for any domain to be using them and to be forwarded to their hosting platform, it should 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 name and the request is then redirected to the DNS servers of the hosting company where the A record of the web site is retrieved, so that you can view the content from the proper location. Commonly 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 only visual.