Goods Receipt 
The Goods Receipt window lets you increase the inventory level in situation that is not the direct result of adding a purchasing document.
When you purchase an item, the warehouse inventory increases automatically when SAP Business One enters the transaction. For example, if you create a goods receipt PO, the warehouse inventory increases accordingly by the specified quantity.
However, purchasing an item is not the only transaction that results in a goods receipt.
Example
For example, you may need to add a goods receipt if you discover during an inventory count that part of the stored quantity has not been taken into consideration. You can enter the overlooked quantity in SAP Business One by adding a goods receipt.
End of the example.