The NS (Name Server) records of a domain name point out which DNS servers are authoritative for its zone. Simply, the zone is the selection of all records for the domain name, so when you open a URL in a browser, your personal computer asks the DNS servers world-wide where the domain is hosted and from which servers the DNS records for the domain address must be retrieved. This way a browser finds out what the A or AAAA record of the domain address is so that the latter is mapped to an Internet protocol address and the web site content is requested from the right location, a mail relay server finds out which server manages the emails for the domain (MX record) so a message can be delivered to the appropriate mailbox, and so on. Any change of these sub-records is done through the company whose name servers are employed, so you can keep the website hosting and change only your email provider for example. Each Internet domain has a minimum of two NS records - primary and secondary, that start with a prefix such as NS or DNS.