Release Qty shows the amount of Qty Open that is counted as Released to warehouse.
Release Qty is automatically set to Open Qty (10) minus any Backorder (7) you enter. Release Qty is calculated when the Pre-release checkbox is set, or the order is Released.
Release Qty is recalculated when the Open Qty is reduced or zeroed by other activity. Saving an order On Hold, editing a Qty, or invoicing an order, all clear the Release Qty.