The Name Servers of a domain point out the DNS servers that deal with its DNS records. The Internet protocol address of the site (A record), the mail server that manages the e-mails for a domain address (MX records), any text record in free form (TXT record), directing (CNAME record) etc are taken from the DNS servers of the website hosting company and for any domain address to be using them and to be forwarded to their hosting platform, it has to have their name servers, or NS records. If you would like to open a site, for example, 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 pointed to the DNS servers of the hosting company where the A record of the website is obtained, so you can see the content from the right location. Ordinarily a domain name has 2 name servers that start with NS or DNS as a prefix and the difference between the two is simply visual.