The NS, or Name Server records of a domain, indicate which servers deal with the Domain Name System (DNS) records for it. Setting the name servers of a specific hosting provider for your domain name is the most convenient way to point 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 forth, so, in case you wish to edit any one of these records, you are going to be able to do it using their system. To put it differently, the NS records of a domain address show 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 name you are attempting to access. This way the website that you will see will be retrieved from the proper location. The name servers normally have a prefix “ns” or “dns” and every single domain address has at least 2 NS records. There's no sensible difference between the two prefixes, so which one a web hosting provider is going to use depends completely on their preference.