The Name Servers of a domain reveal the DNS servers that deal with its DNS records. The IP of the website (A record), the mail server that takes care of 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 hosting provider and for any Internet domain to be using them and to be directed to their hosting platform, it has to have their name servers, or NS records. If you want to open a website, for instance, and you insert the URL, the 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 webhosting provider where the A record of the web site is obtained, enabling you to look at the content from the correct location. Usually a domain name has a couple of name servers that start with NS or DNS as a prefix and the contrast between the two is simply visual.