In process Stock => Stock of current product which is under different warehouse processes but not yet delivered to the end user.
In Picking Stock => Stock of current product which is under picking process (ready for pickup, assigned for picking, assigned for picking or partial picked).
Unusable => Stock quantity which is damaged or not usable.
Usable Stock => Stock quantity is actually available for purchase.
Actual Stock Available for Product => Usable + Unusable + In-Picking Stock
Actual Stock Available for Product => Usable + Unusable + In-Picking Stock