The Name Servers of a domain reveal the DNS servers that handle its DNS records. The Internet protocol address of the site (A record), the mail server that manages 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 web hosting company and for any domain name to be using them and to be pointed to their hosting platform, it has to have their name servers, or NS records. If you would like to open a site, for instance, and you enter the URL, the web browser connects to a DNS server, which keeps the NS records for the domain and the request is then sent to the DNS servers of the hosting company where the A record of the site is retrieved, so that you can see the content from the correct location. Ordinarily a domain name has 2 name servers that start with NS or DNS as a prefix and the distinction between the two is just visual.