XML
or Extensible Markup Language is a language that provides a format
for describing data or documents. The documents must contain structured
information i.e. pictures, words. A markup language is a mechanism
to identify structures in documents. It is different than HTML because
the semantics and tags in HTML are fixed. XML is a most easily defined
as a meta-language for describing markup languages or defining tags
and structural relationships. There is no predefined tag set thus
no preconceived semantics. XML is a part of the World Wide Web Consortium
(W3C) specifications and a subset (application profile) of Standard
Generalized Markup Language (SGML).