Extensible Markup Language (XML) is a simple, very flexible text format derived from SGML (ISO 8879). Originally designed to meet the challenges of large-scale electronic publishing, XML is also playing an increasingly important role in the exchange of a wide variety of data on the Web and elsewhere. http://www.w3.org/XML/
XML is a platform-independent language that can be used for virtually anything, from full databases to small "data islands" on web pages, from sending information between different systems seperated by millions of kilometers to between different parts of the same program.