Domain Name System
The Domain Name System (DNS) is a system used to convert a computer's host name into an IP address  on the Internet. For example, if a computer needs to communicate with the web server example.net, your computer needs the IP address of the web server example.net. It is the job of the DNS to convert the host name to the IP address of the web server. It is sometimes called the Internet's telephone book because it converts a Website's name that people know to a number that the Internet actually uses.