The Name Servers of a domain name reveal the DNS servers that handle its DNS records. The IP address of the site (A record), the mail server that manages the e-mails for a domain address (MX records), any text record in free form (TXT record), pointing (CNAME record) and so on are extracted from the DNS servers of the website hosting provider and for any domain address to be using them and to be directed to their hosting platform, it needs to have their name servers, or NS records. If you want to open a website, for example, and you type in the URL, the web browser connects to a DNS server, which keeps the NS records for the domain name and the request is then redirected to the DNS servers of the hosting company where the A record of the website is retrieved, so you can see the content from the correct location. Ordinarily a domain address has a couple of name servers that start with NS or DNS as a prefix and the difference between the two is only visual.