The Name Servers of a domain name point out the DNS servers that are responsible for its DNS records. The IP address of the website (A record), the mail server that manages the e-mails for a domain address (MX records), any text record in free form (TXT record), directing (CNAME record) etc are taken from the DNS servers of the 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 would like to open a website, for example, 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 forwarded to the DNS servers of the hosting provider where the A record of the web site is retrieved, so you can look at the content from the right location. Ordinarily a domain name has two name servers that start with NS or DNS as a prefix and the contrast between the two is only visual.