OpenDocument or ODF, short for the OASIS Open Document Format for Office Applications, is an open format for saving and exchanging office documents such as memos, reports, books, spreadsheets, databases, charts, and presentations. This standard was developed by the OASIS industry consortium and based upon the XML format originally created by OpenOffice.org. ODF is an ISO and IEC International Standard, ISO/IEC 26300. (from Wikipedia:OpenDocument)
OpenDocument is primarily a file format standard for office suites. A related DocBook format is used for book authoring.