Apre-orderis an order placed for an item that has not yet been released. The idea for pre-orders came because people found it hard to get popular items in stores because of their popularity. Companies then had the idea to allow customers to reserve their own personal copy before its release, which has been a huge success.
Pre-orders allow consumers to guarantee immediate shipment on release, manufacturers can gauge how much demand there will be and thus the size of initial production runs, and sellers can be assured of minimum sales. Additionally, high pre-order rates can be used to increase sales further.