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), directing (CNAME record) etc are obtained from the DNS servers of the web 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 would like to open an Internet site, for example, and you enter the URL, the web browser connects to a DNS server, which keeps the NS records for the domain address and the request is then forwarded to the DNS servers of the hosting provider where the A record of the website is retrieved, so that you can look at the content from the proper location. Usually a domain address has a couple of name servers that start with NS or DNS as a prefix and the difference between the two is just visual.