The Resource Description Framework (RDF) is a foundation for processing metadata; it provides interoperability between applications that exchange machine-understandable information on the Web. RDF describes simple statements about objects and relations between them using some basic types without any structure.
RDF Schema (RDFS) is a special case of RDF, every RDFS document is also an RDF document. RDFS allows generic constructs to define a particular vocabulary.
A RDFS defines the terms that will be used in the RDF statements and gives specific meanings to them.