The XML FAQ

HTML is the HyperText Markup Language (RFC 1866), which started as a small application of question A.4, SGML for the Web, originating with Tim Berners-Lee at CERN in 1989–90.

It defines a very simple class of report-style documents, with section headings, paragraphs, lists, tables, and illustrations, with a few informational elements, but very few presentational elements [10], plus some hypertext and multimedia. See the question on extending HTML. The current recommendation is to use the XML version, XHTML. There is a HTML and XHTML FAQ maintained by Steven Pemberton at http://www.w3.org/MarkUp/2004/xhtml-faq

Recent independent moves by some members of the W3C have led to the development of a revision of HTML currently referred to as HTML5. There is an explanation from Elliotte Rusty Harold, and a FAQ from the WhatWG.