Scumbags... Monthly revenue per active user is estimated at 3 bucks. Now then, go and check how much has been harvested from players in december. It's 32K bucks. Should have been distributed equally between active and passive users and between random visitors.
coin@coin is right. The ARPU (Average Revenue per active User) is calculated : total revenue on a period divided by the number of active users. Of course it's an average meaning some people during the period did nothing and some other are highly addicted.
The average is important because when you do some customer acquisition (advertising) there will be always people who who leaves after 10 minutes and some people who will stay for months. When the acquisition cost is lower than the average revenue then the product does positive performance and more can be invested in acquiring users.
Another important metric is LTV (life time value) total expense of a user during his lifetime with the product.