The term GRAIN FACTORY can be summarized as a facility that processes grain into a usable form. The crossword solution for this term is MILL, which is a building equipped with machinery that grinds grain into flour. Mills have been used since ancient times to process grains such as wheat, barley, oats, and rye into flour. Today, grain factories are used to produce a variety of products, including animal feed, breakfast cereals, and other food products.