Object file

An object file stores program components produced by a compiler or assembler, together with information needed to combine or load them. A relocatable object file commonly contains machine instructions and data divided into sections, named symbols, and relocation records for references whose final locations are not yet known.^[ref]

For example, compiling a file that calls square can produce an object file containing the call-site instruction and an unresolved reference to that symbol. The linker (computing) later supplies its definition from another input. The file thus contains more than the bytes of a self-contained runnable program: its metadata describes how incomplete components fit together.