DNS is abbreviation for Domain Name Service . DNS is an Internet Standard to determine the names of individual machines into IP addresses and vice versa. This resolution is perfomed by machines called nameservers, and these nameservers turn things like the names of web and mail servers into IP addresses.

The Internet functions using IP addresses, not names, so a nameserver is essential if you are going to use a website or mail server.

DNS is a service, not an object. DNS is the process of revolving the name you register into an IP address so that humans can remember the name, and the computers, which use numbers, can translate the name the humans understand into the numbers they understand.