World Centric, a non-profit organization that facilitates community education to "reduce economic injustice and environmental degradation", also has an online Fair Trade/Eco Store with excellent explanations of material content and origin for each class of product.
Their definition of pre-consumer waste is "paper made out of paper scraps and trimmings left over from the paper manufacturing process". In other words, even though it has been recycled, trees were newly cut down to obtain this material.
A startling fact World Centric mentions is that paper makes up 40% of total waste because it is not recycled. By purchasing 100% post-consumer recycled paper, we are creating a demand for paper that would normally end up in a landfill, and no trees are cut down to make it.
So watch your percentages when purchasing paper. 100% recycled can be misleading if only 30% of it is post-consumer.