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 given host company for your domain is the easiest 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), etc, so, in case you need to change some of these records, you will be able to do it via their system. Put simply, the NS records of a domain point out the DNS servers that 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 Internet domain you want to access. That way the website that you're going to see will be retrieved from the right location. The name servers usually have a prefix “ns” or “dns” and each domain name has at least 2 NS records. There isn't any functional difference between the two prefixes, so what kind a hosting provider is going to use depends solely on their preference.