The NS, or Name Server records of a domain, reveal which servers deal with 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 direct it to their system and all its sub-records will be taken care of 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 would like to change any one of these records, you will 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 attempt to open a web address, the DNS servers are contacted to get the DNS records of the Internet domain you want to reach. In this way the site that you're going to see will be retrieved from the right location. The name servers usually 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 which one a web hosting provider will use depends only on their preference.