The Name Servers of a domain name reveal the DNS servers that manage its DNS records. The IP of the web site (A record), the mail server that handles the e-mails for a domain name (MX records), any text record in free form (TXT record), pointing (CNAME record) and so forth are extracted from the DNS servers of the website hosting provider and for any domain name 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 an Internet site, for instance, and you input the URL, the browser connects to a DNS server, which keeps the NS records for the domain name and the request is then forwarded to the DNS servers of the hosting provider where the A record of the website is retrieved, enabling you to view the content from the right location. Commonly a domain address has 2 name servers that start with NS or DNS as a prefix and the contrast between the two is simply visual.