The official business definition of Open Purchase Order (OPO) is an agreement between a buyer and seller that requires the seller to provide goods or services to the buyer at an agreed-upon price and quantity. An OPO authorizes a seller to begin work and become liable for the products or services sold. An OPO is typically created through a purchase order management system, which is used by the buyer to place an order and track its status. The seller receives the OPO, records the order in the system, and then processes the order. The buyer is then responsible for approving the purchase order and releasing payment. An OPO is usually created when the buyer is unable to complete the full amount of the purchase order up front. This could be due to budgetary constraints or a lack of available inventory at the time of purchase. An OPO allows the buyer to pay for the goods or services