The Name Servers of a domain point out the DNS servers that deal with its DNS records. The IP of the site (A record), the mail server that manages the e-mails for a domain (MX records), any text record in free form (TXT record), forwarding (CNAME record) and so forth are extracted from the DNS servers of the 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 wish to open a website, for example, and you type the URL, the Internet browser connects to a DNS server, which keeps the NS records for the domain and the request is then forwarded to the DNS servers of the hosting company where the A record of the site is retrieved, allowing you to look at the content from the correct location. Usually a domain name has two name servers that start with NS or DNS as a prefix and the difference between the two is just visual.