RDF: Resource Description Framework...
It is a framework for metadata; it provides interoperability between applications that exchange machine-understandable information on the Web.
RDF is a method for expressing knowledge in a decentralized world and is the foundation of the Semantic Web, in which computer applications make use of distributed, structured information spread throughout the Web.
The file name extension should be ".rdf"
Simple RDF file looks like
|Books:Book1||dc:title||"Intro about .NET".|
RDF is easy to write, flexible, and unconstraining. It makes it easy to model knowledge and to mesh distributed knowledge sources.