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. For example, in the URL http://www.pcwebopedia.com/index.html, the domain name is pcwebopedia.com.
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. For example:
See "Registering a Domain Name" and "Understanding Internet Governance" in the Did You Know...? section of Webopedia.
See also "Countries and Their Domain Extensions" in Webopedia's Quick Reference Section.