For a particular item, the quantity on order is the total number of items
for which you have written purchase orders but not yet received the items.
QuickBooks automatically keeps track of this number for all the inventory items
in your Item List.
It increases when you write a purchase order for the item. For example, if
you have 30 faucets on order and then discover that you need 20 more,
QuickBooks increases the quantity on order to 50 when you write a purchase
order for the additional 20 faucets.
The quantity on order decreases when you record a bill or item receipt from a vendor for that particular item. For example, if you have 50 faucets on order and then receive 30 of them, QuickBooks decreases the quantity on order to 20 when you record the bill for the 30 faucets. Those 30 faucets are then added to the actual inventory quantity.