A metaformat (or meta format) is a generic low-level file format used as a basis for defining high-level file formats.
Whether a format is a metaformat is ultimately a judgment call. There are no definitive answers to questions like: What is the difference between a container format and a metaformat? Or a serialization format and a metaformat? Is CSV a metaformat, or is it a database or a spreadsheet format? Should TIFF and PDF be considered to be metaformats, given all the subformats of them that have been defined?
Another reasonable, but different, definition of metaformat is "a format that describes other formats". For those formats, see Schema formats.
Formats that implement other formats
- Binary XML
- Boxes/atoms format
- Hamster archive
- ISO Base Media File Format
- Microsoft Compound File
- ODL (NASA Object Description Language)
- Palm OS Database
- Softdisk Publishing UDF files
- XCDL (part of XCL project)
Other "formats about formats"
- Format Policy Registry (FPR) - used by Archivematica to indicate how to handle file formats
- KFP Preflight Profile (for validating PDF files) 
See also Schema formats.