A purchase orer (PO) is a commercial document issued by a buyer to a seller, indicating the type, quantities and agreed prices for products or services the seller will provide to the buyer. Sending a PO to a supplier constitutes a legal offer to buy products or services. Acceptance of a PO by a seller usually forms a once-off contract between the buyer and seller so no contract exists until the PO is accepted. POs usually specify terms of payment, incoterms for liability and freight responsibility, and required delivery date.