A compiler is a computer program that converts the program as written by the programmer, or the "source code" as it is known, into a different form that the computer can understand. This second form is called "object code" and represents very "low-level" instructions that tell the computer's Central Processing Unit to perform very specific and basic functions. This layer of abstraction is important because it means that the same source code can (theoretically at least) be compiled on many different machines using a compiler that knows what instructions to write for each machine.

Object code is an intermediate form of code between the source code and the executable code the computer can run. The object code contains the instructions in the right form, but they need organizing in order to use the computer's memory correctly, and they need to be reconciled with a few other run-time systems...