Domain Name System is the system used on the Internet for mapping of names, such as www.google.com, to IP Addresses such as 216.239.51.99. In many ways you can compare it to a phonebook.

The primary name in an email address; for example, gmail.com and yahoo.com, as well as the domain names for millions of companies and associations. The domain names used for email servers ...

The Address (A) record associates a domain name or subdomain with an IP address, which is the primary purpose of the DNS system ... NS record in the file. THIS DEFINITION IS FOR PERSONAL USE ...