The Name Servers of a domain name point out the DNS servers that handle its DNS records. The IP of the site (A record), the mail server that manages the e-mails for a domain name (MX records), any text record in free form (TXT record), directing (CNAME record) etc are taken from the DNS servers of the web hosting provider and for any domain to be using them and to be pointed to their hosting platform, it has to have their name servers, or NS records. If you want to open a website, for example, and you input the URL, the browser connects to a DNS server, which keeps the NS records for the domain and the request is then sent to the DNS servers of the hosting provider where the A record of the web site is retrieved, enabling you to look at the content from the correct location. Usually a domain address has 2 name servers that start with NS or DNS as a prefix and the difference between the two is just visual.