The Name Servers of a domain name point out the DNS servers that are responsible for its DNS records. The IP address of the website (A record), the mail server that takes care of the emails for a domain (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 company and for any domain name 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 type the URL, the browser connects to a DNS server, which keeps the NS records for the domain and the request is then redirected to the DNS servers of the hosting provider where the A record of the web site is obtained, so you can look at the content from the correct location. Commonly a domain has two name servers that start with NS or DNS as a prefix and the difference between the two is simply visual.