Back order

In my inventory some items are listed as back ordered. (Yet nothing in stock and no orders for these items)

However, if I look at the quantities , it adds up to 0…

Where do these back ordered items come from?

Back orders, come from Sales Invoices where there is no stock available.

Inventory Item ABC has 3 in stock
Sales Invoice sells 5 ABC
ABC now shows Back Order as 2
The number of stock unavailable