The Name Servers of a domain name reveal the DNS servers that handle its DNS records. The Internet protocol address of the web site (A record), the mail server that takes care of the emails for a domain (MX records), any text record in free form (TXT record), forwarding (CNAME record) etc are taken from the DNS servers of the web hosting company and for any domain name to be using them and to be forwarded to their hosting platform, it ought to have their name servers, or NS records. If you would like to open an Internet site, for example, and you enter the URL, the browser connects to a DNS server, which keeps the NS records for the domain and the request is then forwarded to the DNS servers of the hosting company where the A record of the site is retrieved, so that you can look at the content from the correct location. Commonly a domain has a couple of name servers that start with NS or DNS as a prefix and the contrast between the two is simply visual.