The Name Servers of a domain reveal the DNS servers that handle its DNS records. The IP of the web site (A record), the mail server that handles the emails 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 name to be using them and to be forwarded to their hosting platform, it should have their name servers, or NS records. If you would like to open a site, for instance, and you type the URL, the Internet browser connects to a DNS server, which keeps the NS records for the domain and the request is then pointed to the DNS servers of the hosting company where the A record of the web site is retrieved, enabling you to see the content from the correct location. Normally a domain name has 2 name servers that start with NS or DNS as a prefix and the contrast between the two is simply visual.