The Name Servers of a domain point out the DNS servers that are responsible for its DNS records. The IP address 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), directing (CNAME record) and so on are extracted from the DNS servers of the web hosting provider and for any domain address to be using them and to be directed to their hosting platform, it should have their name servers, or NS records. If you want to open an Internet site, for instance, and you insert the URL, the web browser connects to a DNS server, which keeps the NS records for the domain address and the request is then sent to the DNS servers of the hosting provider where the A record of the web site is obtained, so you can view the content from the right location. Normally a domain name has a couple of name servers that start with NS or DNS as a prefix and the distinction between the two is just visual.