A source program processed by a compiler (Assembler, C, COBOL, FORTRAN, PL1 etc.) may exist in either object module format or link and load module format. Object modules (OMs) and link and load modules (LLMs) are the input objects for the Binder Loader System, which generates executable programs from these objects.
The binder links the translated source program to other object modules or link and load modules to produce a loadable unit. To do this it locates the object modules and link and load modules required for the program run and links them. It also resolves cross-references between the modules, i.e. adjusts the addresses which reference fields in other modules (external references) and therefore could not be entered by the compiler at compilation time. This procedure is known as link editing (or binding).
A loader is needed to bring the unit generated by link editing into computer memory. Only then can the program be run.