From XPUB & Lens-Based wiki

Extensible Markup Language

See also HTML and XHTML.

From Charles Goldfarb's ("father of XML") website...

Ed Mosher, Ray Lorie, and I invented the first structured markup language in 1969, IBM's "Generalized Markup Language" (GML). In 1970 I coined the phrase "markup language" in order to describe our invention.

GML led to SGML, which I invented in 1974. SGML literally makes the infrastructure of modern society possible. Our incredibly complex systems and products require massive amounts of documentation -- 4 million pages for a single model of aircraft, for example, which must be updated quarterly. That documentation couldn't be created and managed without SGML.

The same is true for the documentation of nuclear plants, oil rigs, government laws and regulations, military systems -- and anything else that is too complex for a single person to understand and that has life-and-death significance. All of those things are documented with SGML.

From http://charlesfgoldfarb.com/

In 1996, Jon Bosak, Tim Bray, C. M. Sperberg-McQueen, James Clark, and several others began work on a "lite" version of SGML that retained most of SGML's power while trimming a lot of the features that had proven redundant, too complicated to implement, confusing to end users, or simply not useful over the previous 20 years of experience with SGML. The result, in February of 1998, was XML 1.0, and it was an immediate success. Many developers who knew they needed a structural markup language but hadn't been able to bring themselves to accept SGML's complexity adopted XML whole-heartedly. It was used in domains ranging from legal court filings to hog farming.

from http://docstore.mik.ua/orelly/xml/xmlnut/ch01_04.htm