A subscription is when the user decides to select, from DriveWatcher, a resource in Google Drive to receive alerts of any activity that takes place on the selected resource.
The resources that can be monitored are:
What is a DriveWatcher alert?
The alert is the notification that the user receives by email or chat about any activity that has taken place on the resource being monitored.
Is the price calculated based on the number of subscriptions or the number of alerts received?
The price charged on a monthly basis is for the number of subscriptions created and not for the number of alerts received.