Extensible Markup Language is a widely used markup language (as is HTML) designed for sharing documents and data structures. An XML schema defines a document type and the specialized tags used for the data.
XML is open standard defined by the World Wide Web Consortium (W3C) that allows developers to create their own markup tags to describe data. XML-based document formats include XHTML, RSS, Office Open XML and many others.
XML site maps listing URIs and associated metadata are used to inform search engines about pages on a site that are available for crawling.
XML-based microformat schemas are used to make a variety of structured information (personal information, business information, recipes, etc.) available in a standardized format within web pages.
See also: XML site map, XHTML, micorformats