RDF is the semantic web technology used to experess properties of web pages and in general URIs oncluding those representing things outside of the web. RDF is expressed using subject-predicate-object triples, where both the subject and predicate have to be URIs, but the object may also be soem form of literal value such as a number or string. This allows one to express statements such as:
<https://alandix.com/academic/> <ex:is_about> "Alan Dix"
Defined on page 385
Used on pages 166, 385, 428
Also known as resource description framework