The Name Servers of a domain point out the DNS servers that are responsible for its DNS records. The IP of the website (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), forwarding (CNAME record) and so forth are taken 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 has to have their name servers, or NS records. If you wish to open an Internet site, for example, and you input the URL, the web browser connects to a DNS server, which keeps the NS records for the domain address and the request is then sent to the DNS servers of the hosting provider where the A record of the website is obtained, so you can view the content from the correct location. Usually 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.