XML stands for Extensible Markup Language. It is a meta markup language consisting in a set of rules for encoding documents in a format that is both human-readable and machine-readable. XML is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all free to use open standards. XML’s design goals emphasize simplicity, generality, and usability over the Internet. It is a textual data format, with strong support via Unicode for the languages and scripts of the world. RDF/XML is an application of XML, created to express (i.e. serialize) RDF as an XML-document. XML is now widely used.