The Name Servers of a domain point out the DNS servers that handle its DNS records. The IP address of the website (A record), the mail server that deals with the emails for a domain (MX records), any text record in free form (TXT record), directing (CNAME record) etc are extracted from the DNS servers of the website hosting company and for any domain address to be using them and to be directed to their hosting platform, it should have their name servers, or NS records. If you wish to open a website, for instance, and you type in the URL, the browser connects to a DNS server, which keeps the NS records for the domain address and the request is then redirected to the DNS servers of the hosting company where the A record of the website is obtained, enabling you to see the content from the proper location. Commonly a domain has a couple of name servers that start with NS or DNS as a prefix and the contrast between the two is just visual.