What is a process book?

I think Process Book is that show or explain about inside your head and how to get the work's concept. When we creat something we always think about many things, which clours, shapes, material, background, etc... and reserch about thnigs of the works.
what we want to creative? why do we want to creative the one? How do we want to creative?
explaining about these are very important things for making the Process book.