Semantic Web is a term used to describe an effort to make the information on the web more explicitly structured, with well-defined meanings. The well-defined meanings are provided by an ontology (or many ontologies), which defines the objects in a domain and the attributes and relations between those objects, much like you would in a relational database. Much of the work on the semantic web extends earlier work on knowledge representation and reasoning (e.g. expert systems, semantic networks, frames etc), although now built on top of the syntax of XML and the relational foundation of RDF.