The Name Servers of a domain show the DNS servers that manage its DNS records. The IP address of the website (A record), the mail server that deals with the emails for a domain address (MX records), any text record in free form (TXT record), forwarding (CNAME record) and so on are taken from the DNS servers of the website hosting provider and for any domain address to be using them and to be directed 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 insert the URL, the browser connects to a DNS server, which keeps the NS records for the domain address and the request is then pointed 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. Ordinarily a domain address has a couple of name servers that start with NS or DNS as a prefix and the contrast between the two is just visual.