(linkage editor, link loader) A program that combines one or more files containing object code from separately compiled program modules into a single file containing loadable or executable code

This process involves resolving references between the modules and fixing the relocation information used by the operating system kernel when loading the file into memory to run it.

Under Unix, the linker is called "ld" and object files have filename extension .o (object), .so (shared object), or .lib (library), and the resulting executable is called "a.out" by default.