Push back racking is a LIFO(Last-in, First-Out) storage systems, it's designed to organize space by depth , reduce aisle space and increase storage density. In this system, 2-6 deeps pallets can be designed per lane, each pallet stored on wheeled cart that fit on rails .when a forklift put a pallet onto the cart ,it drives forward and the next cart pump out for storing. When removing the pallet from the front cart position, the next cart position will move forward automatically, so that the next pallet can be direct accessed.
link:https://www.safetyshelves.com/racking/push-back-rack/push-back-storage-racks.html