The total revenue divided by the number of transactions of a business, sales channel or other business category.
Average transaction size is they key to analyze the purchasing behaviour of customers. It helps to determine your customer purchasing power and habits. You can then use this metric to design a promotion strategy increase the sales you can make from each customer.
If one retail store has a high number of units sold but a lower than average customer spend, it might be beneficial for it to implement product bundles or up-sell promotions to incentivise additional spending.