06 December 2011
I suppose you are asking about open Purchase Order.
Let us suppose you want to purchase 10 machineries from 1 vendor. All the 10 cannot be supplied together and there will be a time gap between supply of machineries.
In this case, instead of creating 10 different POs, only 1 PO is created. This PO will be valid until all the 10 machineries have been supplied.
So, even after receipt of 1 machinery, the PO will remain open.