The Name Servers of a domain name reveal the DNS servers that deal with its DNS records. The IP of the website (A record), the mail server that manages the e-mails for a domain address (MX records), any text record in free form (TXT record), pointing (CNAME record) etc are extracted from the DNS servers of the web hosting provider and for any domain address to be using them and to be forwarded to their hosting platform, it ought to have their name servers, or NS records. If you wish 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 name and the request is then sent to the DNS servers of the webhosting provider where the A record of the web site is obtained, so you can see the content from the proper location. Ordinarily a domain address has two name servers that start with NS or DNS as a prefix and the difference between the two is simply visual.