A Blanket Order is a purchase order; is a contract between the customer and supplier to supply goods (usually is expandable goods and recurring) at a predetermined price over an agreed period.
Assuming you are a manufacturer and require to use a large quantity of a product each month. You may issue a blanket order to the supplier to supply the goods at a predetermined price on a regular basis instead of having to negotiate the price and send a purchase order monthly. A Blanket Order help to cut down the administrative cost, control price fluctuation, ensure stock availability and reduce the storage cost; it is a just-in-time system. To the supplier, on the other hand, have a better sales forecast and better allocation of resources.
You need to process the purchase order whenever goods received. The purchase order will remain as an open order until fully fulfiled. There are reports available in MoneyWorks accounting system which helps to monitor the backorder, inventory, and purchases; or you may use the enquiries feature to check the movement of each product.