Wiktionary
paper mill
n. 1 A factory devoted to making paper from wood pulp and other ingredients. 2 An organization that unethically sells pre-written papers to students.
WordNet
paper mill
n. a mill where paper is manufactured
Wikipedia
Paper mill
A paper mill is a factory devoted to making paper from vegetable fibres such as wood pulp, old rags and other ingredients using a Fourdrinier machine or other type of paper machine.