What Is RDF?

RDF was originally created in 1999 as a standard on top of XML for encoding metadata--literally, data about data. Metadata is, of course, things like who authored a web page, what date a blog entry was published, etc., information that is in some sense secondary to some other content already on the regular web. Since then, and perhaps especially after the updated RDF spec in 2004, the scope of RDF has really evolved into something greater. The most exciting uses of RDF aren't in encoding information about web resources, but information about and relations between things in the real world: people, places, concepts, etc.

Tauberer, Joshua. XML.com (2006). Articles>Information Design>XML>Metadata