What is a postprocessor?

The term postprocessor, sometimes referred to as a "post," basically means a translator.

Picture a job foreman who speaks English. He needs to instruct his worker, who speaks Spanish, how a certain project should be done. So, he uses a human to communicate his instructions to his worker.

Think of the CAM software as that job foreman. The machine is the worker. The postprocessor is the translator.

In more technical terms, the postprocessor contains the instructions needed to translate design and toolpath information from a software's native language into the language a CNC machine uses to accept instructions.