Object file

An object file is a file containing object code, meaning relocatable format machine code that is usually not directly executable. There are various formats for object files, and the same object code can be packaged in different object files. An object file may also work like a shared library.

In addition to the object code itself, object files may contain metadata used for linking or debugging, including: information to resolve symbolic cross-references between different modules, relocation information, stack unwinding information, comments, program symbols, debugging or profiling information.

An object file format is a computer file format used for the storage of object code and related data.

There are many different object file formats; originally each type of computer had its own unique format, but with the advent of Unix and other portable operating systems, some formats, such as COFF and ELF have been defined and used on different kinds of systems. It is possible for the same file format to be used both as linker input and output, and thus as the library and executable file format.

The design and/or choice of an object file format is a key part of overall system design. It affects the performance of the linker and thus programmer turnaround while developing. If the format is used for executables, the design also affects the time programs take to begin running, and thus the responsiveness for users.

...
Wikipedia