LineItem Object properties: how to query the actual sold quantity of an Order LineItem

Hi,

I need to query the actual number of LineItems of an order i. e.

Number of initially ordered items - Number of returned items

The API provides :

quantity

currentQuantity

refundableQuantity

Quantity is the number of ordered items.
But, what is the difference between current and refundable, if there’s any?

Thanks

Deniz