What is difference between RDF and RDFS?

• RDF, RDFS, and ontology are not interchangeable terms. RDF (Resource Description Framework), is a conceptual data model which can be rendered physically (serialized) using various formats such N3, Turtle, RDF/XML, etc.
• RDFS (RDF Schema) is "a general-purpose language for representing simple RDF vocabularies on the Web."
• The elements of RDFS can be used to construct an ontology. Of course, if you want more expressive power for ontology and you need to encode some properties that cannot be done using RDFS elements, you always have the OWL option.
• RDFS has more expressive power than RDF. OWL in turn has more expressive power than RDFS.