XML: XML stands for "extensible markup language." A markup language is a system for annotating an online document in a way that is syntactically distinguishable from the text. Accordingly, XML is a simple, flexible text format that is readable by both humans and machines, which is used to describe, rather than display, information. As a result, XML is best described as a tool for carrying information that is independent of software and hardware. Originally derived from the Standard Generalized Markup Language (SGML), which defines generalized markup languages for documents, XML is used to make it easy to syndicate or format information using a number of basic publishing systems.

XML was compiled by 11 members of the XML Working Group, which were supported by an Interest Group with over 150 members. Interestingly, the group never met face-to-face, preferring to design via email and weekly teleconferences. Despite this, XML was successfully released in 1998 after several years of work. Today, XML is used in a number of common software products and applications. For example, Microsoft Office, OpenOffice.org, and Apple iWork all use XML. However, XML has been criticized for its complexity, and some have even refuted claims that XML is a self-describing language, although XML specification itself does not claim to be such a thing.