Domain names are used to identify one or more IP addresses. For example, the domain name microsoft.com represents about a dozen IP addresses. Domain names are used in URLs to identify particular Web pages.
Every domain name has a suffix that indicates which top level domain (TLD) it belongs to. There are only a limited number of such domains.
gov – Government agencies
edu – Educational institutions
org – Organizations (nonprofit)
mil – Military
com – commercial business
net – Network organizations
ca – Canada
au – Australia
Because the Internet is based on IP addresses, not domain names, every Web server requires a Domain Name System (DNS) server to translate domain names into IP addresses.