A binary object file is an object file that contains absolutely no headers, neither for Windows nor Linux. This format is needed if you want to create a bootloader for instance, or something else that is to be run by BIOS, as the BIOS can only read this format.

It can be considered to be a "raw", "flat" binary, as no relocations are present, and external symbol references are not allowed. This can be used for programs that need not any Operating Systems and do not use any of their services.