The Name Servers of a domain show the DNS servers that handle its DNS records. The Internet protocol address of the website (A record), the mail server that deals with the e-mails for a domain (MX records), any text record in free form (TXT record), pointing (CNAME record) etc are taken from the DNS servers of the website hosting company and for any domain name to be using them and to be directed to their hosting platform, it needs to have their name servers, or NS records. If you want to open a website, for example, and you insert the URL, the browser connects to a DNS server, which keeps the NS records for the domain and the request is then pointed to the DNS servers of the webhosting provider where the A record of the website is retrieved, allowing you to view the content from the proper location. Commonly 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.