A purchase order is a written authorization from a buyer to acquire goods or services. The document authorizes a supplier to deliver to the buyer at the price, quality level, delivery date, and certain other terms specified in the agreement. A purchase order is legally binding after the supplier counter-signs it.
A purchase order is time-consuming to create. To reduce the work load, some organizations issue a master purchase order to each supplier, authorizing considerably more than is initially needed, and then issue releases against the master purchase order.