The Name Servers of a domain name reveal the DNS servers that handle its DNS records. The IP of the site (A record), the mail server that takes care of the emails for a domain name (MX records), any text record in free form (TXT record), pointing (CNAME record) etc are taken from the DNS servers of the web hosting provider and for any domain 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 an Internet site, for instance, 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 sent to the DNS servers of the webhosting provider where the A record of the web site is obtained, enabling you to view the content from the proper location. Normally 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 simply visual.