Extensible markup language (XML)
From The Glossary of Digital Photography
A method of marking data that is designed to allow sharing of information across different computer platforms and systems. XML is especially useful for systems connected across the World Wide Web. It is not really a language; it is a set of rules of ways to organize and tag data so that a variety of computer systems can understand that data. It is often used to create customized vocabularies known as XML schemas. By referring to the particular XML schema document, anyone can understand the data, and software can manipulate it. The World Wide Web Consortium, also known as W3C, developed it in 1996. An XML schema is used by programs, such as Apple's Aperture, to define how they store and order metadata with a series of tags in their metadata files. See also metadata
