Here is a link to a FAQ, tutorials, examples, and articles on the Resource Description Framework (RDF).
http://www.xml.org/xml/resources_focus_rdf.shtml
The W3C (http://www.w3.org/RDF/FAQ) describes RDF as:
RDF--the Resource Description Framework--is a framework for metadata; it provides interoperability between applications that exchange machine-understandable information on the Web. RDF emphasizes facilities to enable automated processing of Web resources and as such provides the basic building blocks for supporting the Semantic Web.