XML (Extensible Markup Language) is a group of rules for programming files so it can be read by any XML-compatible application.

XML is designed to highlight simplicity and usability over the internet.  It is the most common tool for information communication between various kinds of applications.  Although the XML model centers on documents, it is generally used for the representation of random data structure, such as in web services.

Various application programming interfaces are used by software developers to process XML data.  Systems are also available to help in the definition of XML languages.

Hundreds of XML-based languages have been produced, including XHTML, RSS, and Atom.  Many office-productivity tools use XML-based formats as their default, such as Microsoft Office, OpenOffice.org, and Apple’s iWork.

XML is sometimes confused with HTML, which were both designed for different purposes.  XML was created to carry and store data, whereas HTML was made to display information.  Therefore, XML is not a replacement for HTML, but a complement.