The Name Servers of a domain point out the DNS servers that manage its DNS records. The IP address of the web site (A record), the mail server that deals with 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 website hosting provider and for any domain to be using them and to be pointed to their hosting platform, it needs to have their name servers, or NS records. If you would like to open an Internet site, for instance, and you enter the URL, the browser connects to a DNS server, which keeps the NS records for the domain and the request is then redirected to the DNS servers of the webhosting provider where the A record of the website is obtained, so you can see the content from the right location. Ordinarily 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.