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 handles the emails for a domain (MX records), any text record in free form (TXT record), pointing (CNAME record) and so forth are obtained from the DNS servers of the hosting company and for any domain to be using them and to be directed to their hosting platform, it has to have their name servers, or NS records. If you would like 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 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. Usually a domain has 2 name servers that start with NS or DNS as a prefix and the distinction between the two is only visual.