UNDEFINED File - opening and understanding

Did your computer fail to open an UNDEFINED file? We explain what they are used for and recommend software that we know can open or otherwise handle your .UNDEFINED files.

What is an UNDEFINED file?

The .undefined file extension is used for various file formats that cannot be recognized by the system. Some file recovery tools use this file extension to label recovered files that have not been completely restored. Other programs like Web browsers and email applications may label downloaded or attached files with unknown file types as UNDEFINED files.The content of these .undefined files varies, depending on the actual format of the files. For example, a data recovery application that has failed to completely restore a JPG file may label the file as an UNDEFINED file, and this .undefined file may contain corrupted image data. On the other hand, a Web browser that fails to recognize an AVI file that has been downloaded from the Internet may label the digital video file as an UNDEFINED file. This .undefined file may contain digital video, but there is no guarantee that the .undefined file will play in a standard AVI player.It's best to leave these .undefined files alone. In most instances, these UNDEFINED files contain corrupted data and are from unknown sources.

How to open UNDEFINED files

You will need a program compatible with the specific file you are trying to open, as different programs may use files with file extension UNDEFINED for different purposes.

While we have not verified the apps ourselves yet, our users have suggested 2 different UNDEFINED openers which you will find listed below.

Suggest another file format using extension UNDEFINED

While we know of one file format using the .UNDEFINED file extension, there may be more. It is widespread that different programs use files with the same file extension for very different types of data. Please let us know if you are aware of a different kind of .UNDEFINED file.

Various viewers for this file format

These apps are known to open certain types of UNDEFINED files. Remember, different programs may use UNDEFINED files for different purposes, so you may need to try out a few of them to be able to open your specific file.

KMPlayerKMPlayerUser submitted
GOM PlayerGOM PlayerUser submitted
We have not verified any software that we know for certain will work with UNDEFINED-files on Mac. If you know one, please use the 'Suggest a program' link below and tell us about it!
We have not verified any web services that we know for certain will work with UNDEFINED-files. If you know one, please use the 'Suggest a program' link below and tell us about it!