Nothing complicated! Whenever a card is used anywhere - be it an online site, at a mall, or at an ATM machine, it gets tracked on your Open dashboard as a transaction.
On the other hand, reversed transactions are the ones that get refunded to your card from the merchant. For e.g., say you ordered 5 laptops for your company from Amazon India and after receiving it, 2 of them aren't working. You ask for a refund. The amount processed by Amazon India will then be credited back to your Open card. This is known as a reversed transaction.