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 particular hosting provider for your domain is the most effective 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 would like to edit some of these records, you're going to be able to do it by using their system. Put simply, the NS records of a domain show the DNS servers which are authoritative for it, so when you try to open a web address, the DNS servers are contacted to get the DNS records of the domain you want to access. This way the site you'll see will be retrieved from the correct location. The name servers normally have a prefix “ns” or “dns” and every single domain name has at least two NS records. There's no functional difference between the two prefixes, so what type a hosting provider is going to use depends solely on their preference.