Average Orders per Month measures the number of orders from customers you've received on average. It can be used to estimate your order volume and is useful to predict upcoming months.
Since the number of orders can fluctuate from month-to-month and over a year's cycle, it is useful to use at least a year's order data. That will allow the averaging to smooth out any highs/lows.
Eric Davis
Market to your customer's timing
Figure out how long customers wait in-between purchases and you have a key component for your marketing timing. This is the basis of the Average Latency metric and Order Sequence Report in Repeat Customer Insights.