This is an abbreviation that usually refers to “Active Customers” or customers who are in contract or paying a subscription for your business.

For free users of your service “Actives” also refers to those customers who have a continuing relationship with your company. Since no money is changing hands it is calculated for a set period, where any customer returning to your app or website in the last 30 days is included. That is then reported as your “30 Day Actives” KPI. The choice of period is up to you, as some businesses have very frequent visitors, and others perhaps only return occasionally. 7, 14, 30, 90 day active metrics are common.