CPO, or Cost per Order, is a metric used in Facebook ads to measure the average marketing spend required to drive any purchase to your store, including both new and returning customers. This metric is crucial for businesses to understand as it helps them determine the effectiveness of their advertising campaigns and how much they are spending to acquire each customer. By tracking CPO, businesses can optimize their ad spend and adjust their strategies accordingly to ensure they are getting the most bang for their buck. It's important to note that CPO can vary depending on your industry, target audience, and advertising goals, so it's essential to monitor this metric regularly to ensure you are meeting your business objectives.