The Semantic Web is an extension of the World Wide Web through standards set by the World Wide Web Consortium (W3C). The goal of the Semantic Web is to make Internet data machine-readable.
This can be seen in various aspects of web development, one being semantic HTML as a way to give your markup meaning, microformats like schema.org or linked-data like json-ld. Another aspect is from the opposite perspective: Reading and interpreting data. This can be done with metadata via RDF.
Created by Tim Berners-Lee, James Alexander Hendler, Ora Lassila