XML - EXtensible Markup Language

EXtensible Markup Language (XML) is an open standard for describing data from the W3C. It is used for defining data elements on a Web page and business-to-business documents. XML uses a similar tag structure as HTML. However, whereas HTML defines how elements are displayed, XML defines what those elements contain.

While HTML uses predefined tags, XML allows tags to be defined by the developer of the page. Thus, virtually any data items, such as "product," "sales rep" and "amount due," can be identified, allowing Web pages to function like database records. By providing a common method for identifying data, XML supports business-to-business transactions and has become "the" format for electronic data interchange and Web services.