The Semantic Web, as the name implies, would feature software that enables computers to act as though they understand what words mean:
Extensible markup language. A method of coding, or tagging, Web pages so that computers can distinguish specific types of content. XML tags tell whether an item is a picture, an audio file, a piece of text, or numerical data--but don't explain the specific meaning. Instead, they point to where that information can be found, usually an RDF entry.
Resource Description Framework. Essentially, this is a combination dictionary and thesaurus for XML tags. It allows computers to understand the syntax of information on Web pages. But even this level still falls short of real, semantic understanding. For that, RDF definitions will require links to something called an ontology.
A sort of encyclopedia that lays out the detailed relationships among XML terms and RDF concepts. Computers can't think the way humans do. But ontologies will help them understand XML tags and make decisions--for example, whether or not all the conditions are in place to execute a commercial transaction. This is the capstone of the Semantic Web.