What is the difference between Active Subscribers and Active Subscriptions?

The Active Subscribers figure within the Subscribers dashboard does not count individual subscriptions, but rather subscribers. 

What this means is - if one subscriber has more than one subscription active on their account, they will still only count as ONE subscriber for that figure since it counts active subscribers, not the multiple subscriptions that may be active within one subscriber's account. 

The Active Subscriptions figure within the Plans dashboard DOES count individual subscriptions, including multiple ones per individual account, so if you need to see how many active, individual subscriptions are active on your site, then this figure would be a better option.