XML (eXtensible Markup Language) comes virtually unchanged from the ISO 8879 standard SGML for the implementation of markup languages. It is a general purpose specification that aims at representing with simplicity documents with high quality and usability.
Examples of markup languages coming from xml are xhtml, mathml, musicml, graphml and svg. Applications like OpenOffice use the ooxml file format to represent word processing documents, spreadsheets, presentations and charts. This file format is essentially a zip file containing xml documents.
Although it is very similar to xhtml, the html specification is not a xml markup language.