Generally, a "domain name" is the registered "www" name or "web address" of a web site.
Specifically, Webster's Dictionary of Computer Terms has these definitions:
A "domain name system" is defined as:
In the Internet, the conceptual system, standards, and names that make up the hierarchical organization of the Internet into named domains.
and a "domain name":
In the system of domain names [a domain name is] used to identify individual Internet computers, a single word or abbreviation that makes up part of a computer's unique name [such as blackwellwebdesign.com]. ... At the end of the series of domain names is the top level domain (here, "com") ....
Both definitions are from Webster's New World Dictionary of Computer Terms, Seventh Edition.
We have found that "domain name," "URL," and "web address" are usually used by the general public interchangeably.
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The Website 101 pages are basic informational pages to provide an overview of some of the more standardized functions of most web sites.
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