---
title: "Purchase order (PO): definition | Rex glossary"
description: "A buyer-issued document authorizing a purchase at agreed quantities and prices. Many buyers won't pay an invoice that doesn't reference a valid PO."
canonical: https://www.rex.inc/glossary/purchase-order
---

# Purchase order (PO)

A buyer-issued document authorizing a purchase at agreed quantities and prices. Many buyers won't pay an invoice that doesn't reference a valid PO.

The PO is the buyer's commitment and their AP team's reference point. Invoices are matched against it, so a missing PO number, an expired PO or a line that exceeds the PO's remaining balance can stop payment.

Catching PO problems before an invoice goes out, by checking orders against PO terms, quantities and billing requirements, is far cheaper than resolving a rejection afterwards.

How Rex helps

Order & PO readiness

Validate orders against POs, terms, and billing requirements.

[See how it works](https://www.rex.inc/order-po-readiness)

## Related terms

- [Three-way match An accounts payable control that checks an invoice against the purchase order and the receiving record before approving it for payment.](https://www.rex.inc/glossary/three-way-match)
- [Procure to pay (P2P) The buyer's side of the transaction: requesting and purchasing goods, receiving them, then matching and paying the supplier's invoice.](https://www.rex.inc/glossary/procure-to-pay)
- [AP portal A buyer-run website, such as Coupa, Ariba or a retailer's own system, where suppliers must submit invoices and track their status to get paid.](https://www.rex.inc/resources/customer-portals/ap-customer-portals-guide)
- [Invoice dispute A customer's objection to an invoice, for example to its price, quantity, terms or delivery, that holds up payment until it's resolved.](https://www.rex.inc/glossary/invoice-dispute)

Next step

Accelerate your receivables operation with Rex

A short walkthrough of agents working your accounts under your guardrails, with your team on the exceptions.

[Learn more](https://www.rex.inc/learn-more)

[Back to the glossary](https://www.rex.inc/glossary)