Pre-consumer recycled goods?

Can anyone tell me what the difference between **pre-**consumer and **post-**consumer recycled goods are? An example is in artist materials, where you can buy sketch paper pads in either format. It might seem kinda obvious, but does it actually mean that some paper is produced from products that never actually sold (maybe just sitting in a warehouse forever?). (I understand post-consumer is collected from those recycle bins full of newspapers and such.)

I believe that "pre-"consumer products come from industry waste and non used products so they are much easier to process (no slimy pizza waste on the pizza boxes) and post from peoples recycling boxes.

Industry also uses much larger quantities of similar materials, so you end up with a larger amount of homogeneous paper and pulp.

“Pre-consumer” are the leftovers from the paper-making process that remain in the factory. When paper is cut, there are always scraps left over, or pieces that don’t meet quality control standards, for example. These are what are recycled.

“Post-consumer” is what has actually been in the hands of the consumers and returned via recycling programs.