The Name Servers of a domain reveal the DNS servers that are responsible for its DNS records. The IP of the website (A record), the mail server that manages the emails for a domain address (MX records), any text record in free form (TXT record), pointing (CNAME record) and so on are taken from the DNS servers of the hosting company and for any domain address to be using them and to be forwarded to their hosting platform, it should have their name servers, or NS records. If you would like to open an Internet site, for instance, and you input the URL, the browser connects to a DNS server, which keeps the NS records for the domain address and the request is then pointed to the DNS servers of the hosting provider where the A record of the website is obtained, so you can view the content from the right location. Commonly a domain has 2 name servers that start with NS or DNS as a prefix and the difference between the two is just visual.