When exporting your orders, you will have two columns that will indicate any promotional discounts that were applied to the orders via the Promotion Manager.
One column is labeled odiscount and is used to indicate discounts that were applied to the order from an automatic promotion. In other words, a promotion that was automatically applied to the order based on the promotion rules.
The other column is named ocoupon, and is used to indicate discounts that were applied by the promotion using a coupon code. In other words, a promotional discount that required the shopper to enter a code at the checkout pages to receive the advertised discounts.
If using stacked promotions, both columns should always be considered when determining the total discount applied to your orders.
The "odiscount" column also applies to manual discounts applied to the order when using the Phone Order function.
Similarly, the "ocoupon" column also has a secondary application for times when the order has a gift certificate payment used on it.