The NS, or Name Server records of a domain name, show which servers handle the Domain Name System (DNS) records for it. Setting the name servers of a particular hosting provider for your domain address is the most effective way to point it to their system and all its sub-records are going to be managed 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 change 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 address 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 retrieve the DNS records of the domain name you are attempting to reach. That way the site that you're going to see will be retrieved from the correct location. The name servers usually have a prefix “ns” or “dns” and every single domain has at least two NS records. There is absolutely no practical difference between the two prefixes, so which one a web hosting provider is going to use depends entirely on their preference.