A purchase order before invoice is an official document created by a buyer to identify what goods or services they intend to purchase from a vendor. It serves as a legally binding agreement between both parties that details the total cost, quantity, and quality of the items being purchased. It also outlines payment terms and conditions such as when payment is due and any discounts that may apply. By issuing a purchase order before an invoice is received, the buyer can better control their budget and ensure that they are only paying for goods or services rendered. This reduces the risk of potential disputes and helps maintain positive relationships with vendors.