Some Purchase Orders/RFQs issued by the Department of Defense are assigned priority ratings, under a system known as the Defense Priority Allocation System, or DPAS. DX-rated orders have the highest priority. DO-rated orders have a lower priority than DX, but still have priority over unrated orders.
If you receive a PO with a DPAS rating, you must accept the order, as long as you can meet the required delivery date. A DX or DO-rated order must be given priority over other orders.