A set of markup formats for word-processing, spreadsheet, and presentation files, packaged as a zip of markup parts. Microsoft developed the formats so software can store a document as separate files instead of one opaque binary stream.
Each of those parts is written in eXtensible Markup Language (XML). Ecma International standardized an early version, and the formats were also published as an international standard. This family is the successor to the older binary office files.
How the Package Is Built
A word-processing file uses the .docx suffix for one such package. Spreadsheet and presentation files follow the same idea: a zip whose members are markup parts, plus any embedded media the document needs.
- Document parts. Text, styles, and relationships sit in separate members of the archive rather than in a single binary record.
- Readable structure. A tool can open the zip, inspect one part, and leave the rest untouched.
- Shared packaging. Spreadsheet cells and presentation slides use the same zip-of-parts approach as the word-processing file.
What Each File Kind Stores
The three everyday packages differ by the kind of content they hold, not by the packaging method.
| Kind | What the Package Stores |
| Word processing | Text, styles, and related parts, using the .docx suffix |
| Spreadsheet | Cells, formulas, and sheets as markup parts |
| Presentation | Slides and supporting parts in the same zip |
From Binary Files to a Published Standard
Older office software wrote the same kinds of documents as binary files. Those files were compact, but another program could not reliably pull out a paragraph, a cell, or a slide without the original application. A zip of markup parts makes each piece a file another tool can open. Ecma International’s early standard, and later publication as an international standard, turned Microsoft’s formats into a shared way to store those documents.