Extensible Markup Language (XML)

A markup language that defines rules of document formatting and encoding that is both human and machine readable. Designed to enable the use of SGML on the World Wide Web, XML is a regular markup language that defines what you can do (or what you have done) in the way of describing information for a fixed class of documents (like HTML). XML goes beyond this and allows you to define your own customized markup language. It can do this because it is an application profile of SGML. XML is a metalanguage, a language for describing languages.