The NS (Name Server) records of a domain name point out which DNS servers are authoritative for its zone. In simple terms, the zone is the collection of all records for the domain name, so when you open a URL inside an Internet browser, your computer asks the DNS servers worldwide where the domain name is hosted and from which servers the DNS records for the domain should be retrieved. In this way a browser finds out what the A or AAAA record of the domain name is so that the latter is mapped to an Internet protocol address and the site content is requested from the correct location, a mail relay server finds out which server deals with the e-mails for the domain name (MX record) so a message can be sent to the appropriate mailbox, etc. Any change of these sub-records is conducted using the company whose name servers are used, enabling you to keep the website hosting and change only your email provider for instance. Each domain name has no less than two NS records - primary and secondary, that start with a prefix such as NS or DNS.