Université Catholique de Louvain: Olivier Bonaventure's "Computer Networking: Principles, Protocols, and Practice"
Read section 3.2.1, "The Domain Name System," on pages 32-37.
In order to access a website, you need to know the website's IP address. IP addresses can be somewhat cumbersome and difficult to remember, since they are simply four numbers separated by periods (e.g., 120.755.3.9). The Domain Name System (DNS) is the application that has solved this problem by allowing us to use "human readable" names for websites. What is the domain name for your home page on your work, school, or home LAN? What is the IP address for each one? Which would you rather use - the IP address or the domain name?