The Stacks are Wade Owen Watt's home prior to finding the Easter Egg in OASIS.
The stacks are dozens of trailers stacked on top one another and are held together by metal beams. They were created to save space, labor, and resources. This cheap construction caused the over crowded homes to become a breeding ground for theft, murder, molestation and other heinous activities.
The book refers to The Stacks being on the western outskirts of Oklahoma City , with Wade living in the Portland Avenue Stacks. The movie trailer, however, implies that The Stacks are in Columbus, Ohio.