Unplanned inventories (stock) : It refers to change in stock which has incurred unexpectedly due to unexpected fall in sales. Firm have unsold goods. For example, if a firm has opening stock of 200 unit and it wants to raise its stock from 200 to 400 units and expects sales to be 1000 units it will produce 1200 if the end of the year it is found actual sales were 900 units then closing stock will be :
Opening Stock + Production - Sale
=200+1200−900
=500‌ units ‌
This was not unexpected that is called unplanned inventory.