MAU = Monthly Active Users. An MAU is a unique Monthly Active User by device.
For example, if you were to open up your Facebook app on your iPhone 30 times in February, the MAU would be 1. Now if you opened up the Facebook app on your iPhone 30 times and you opened up the Facebook app on your iPad 15 times in the month of February, the MAU would be 2. That’s because you used two devices to access the app.
Helpshift calculates MAU based on the amount of visitors per month. This counts for all users who open your any of your apps, not just those who submit Issues via Helpshift.
Your MAU quota is visible on your billing page with purchase of a Pro or Starter account.