What is a domain name?

The Domain Name System completes the task of matching domain names to IP (Internet Protocol) addresses. Domain names, and their corresponding IP addresses, must be unique. If more than one organization on the Internet had the same domain name, confusion would occur when the network tried to identify and communicate with the computers within those organizations.

For example, if there were two separate universitites, one in Maine and one in Arizona, they cannot both use the domain name "coolschool.edu", because the Domain Name System would not know which one of the universities' IP addresses were associated with that domain name.