An XML-based file format developed by Microsoft and standardized by ECMA (ECMA 376). It is the default document format for saving applications in Microsoft Office starting with Office 2007.
See Office file formats
A Package of Folders and Files
An Office Open XML (OOXML) document is a zipped collection of folders, subfolders, XML files and other file types, which is a huge contrast from previous Microsoft Office and traditional business file formats. One advantage of the Office Open XML structure is that various parts of the document can be edited more easily because they reside in separate files.
For comparison, following are the file structures created in both the traditional Word format (Word 2003 and prior) and Word Open XML format (starting with Word 2007). The two examples depict a simple document with one picture saved with the name RESUME.
#1 - TRADITIONAL WORD DOCUMENT
resume.doc (one file)
#2 - OFFICE OPEN XML WORD DOCUMENT
resume.docx (one file, which is a
zipped collection of the
following folders & files)
.rels (RELationshipS; pointers to
app, core and document
app.xml (page characteristics)
core.xml (authorship, versions)
document.xml (text content)
settings.xml (spelling, grammar,
styles.xml (paragraph styles)
webSettings.xml (browser attributes)
document.xml.rels (pointers to
image1.jpeg (embedded image)
theme1.xml (foreign language