The NS, or Name Server records of a domain, reveal which servers deal with the Domain Name System (DNS) records for it. Setting the name servers of a given hosting provider for your domain name is the most convenient way to direct it to their system and all its sub-records are going to be handled on their end. This includes A (the IP address of the server/website), MX (mail server), TXT (free text), SRV (services), CNAME (forwarding), and so on, so if you would like to change any of these records, you're going to be able to do it through their system. In other words, the NS records of a domain reveal the DNS servers that are authoritative for it, so when you attempt to open a web address, the DNS servers are contacted to get the DNS records of the domain you are trying to reach. That way the website you will see will be retrieved from the correct location. The name servers normally have a prefix “ns” or “dns” and each and every domain address has at least 2 NS records. There isn't any sensible difference between the two prefixes, so what kind a host company is going to use depends only on their preference.