It's All About The Deliverables

Paul Ritchie mentions a previous post.
The simple concept is that deliverables is what the customer bought. Whether it is a machine that can fly to the Space Station and return or a piece of software that can do something for the business.
"Done" means the desired deliverable in delivered. If the Plan and the associated schedule don't describe how these deliverables will be delivered, then it's going to be tough finding out if progress is being made.