The Name Servers of a domain point out the DNS servers that handle its DNS records. The IP of the website (A record), the mail server that handles the e-mails for a domain name (MX records), any text record in free form (TXT record), forwarding (CNAME record) and so forth are extracted from the DNS servers of the website hosting company and for any domain name 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 a 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, allowing you to look at the content from the correct location. Ordinarily a domain name has a couple of name servers that start with NS or DNS as a prefix and the distinction between the two is just visual.