The tooltip next to "Active Devices" and "Active Last 30 Days" says
The total number of devices with at least one session during the selected period
and
The total number of devices with at least one session within 30 days of the selected day" >respectively.
Next to those, it defines another metric called "Sessions" as
The number of times the app has been used for at least two seconds.
What does apple mean by a "device with at least one session during the selected period"? Is it referring to a device that was merely booted, or a device on which our app was launched during the selected period? I haven't been able to find any clarification on that.
On google play connect "Active devices" refers to devices that were active (no matter whether the app was fired during that period).