The Name Servers of a domain show the DNS servers that manage its DNS records. The IP of the web site (A record), the mail server that deals with the emails for a domain (MX records), any text record in free form (TXT record), directing (CNAME record) and so forth are obtained from the DNS servers of the website hosting provider and for any domain to be using them and to be pointed to their hosting platform, it needs to have their name servers, or NS records. If you want to open a site, for instance, and you enter the URL, the browser connects to a DNS server, which keeps the NS records for the domain name and the request is then pointed to the DNS servers of the hosting provider where the A record of the web site is obtained, so that you can see the content from the right location. Normally a domain name has a couple of name servers that start with NS or DNS as a prefix and the difference between the two is simply visual.