The Name Servers of a domain point out the DNS servers that deal with its DNS records. The IP address of the web site (A record), the mail server that manages the emails 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 company and for any domain to be using them and to be pointed to their hosting platform, it should have their name servers, or NS records. If you wish to open a site, for example, and you insert the URL, the Internet browser connects to a DNS server, which keeps the NS records for the domain name and the request is then forwarded to the DNS servers of the webhosting provider where the A record of the web site is retrieved, enabling you to look at the content from the proper location. Commonly a domain name has 2 name servers that start with NS or DNS as a prefix and the distinction between the two is only visual.