The NS, or Name Server records of a domain, reveal which servers manage the Domain Name System (DNS) records for it. Setting the name servers of a particular host company for your domain is the most convenient way to point it to their system and all its sub-records will 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 forth, if you wish to edit any of these records, you will be able to do it through their system. In other words, the NS records of a domain address point out the DNS servers which are authoritative for it, so when you try to open a web address, the DNS servers are contacted to retrieve the DNS records of the domain you want to access. That way the site you will see is going to be retrieved from the right location. The name servers typically have a prefix “ns” or “dns” and every single domain address has at least two NS records. There's no sensible difference between the two prefixes, so which one a website hosting provider will use depends completely on their preference.