Trials for a given period are the number of subscription activations with a free trial period.
Users can turn off subscription renew while being in a Trial. Technically they are still subscribers, but they won't convert to a paid customer. It's important to know how many users won't prolong trial as it affects your payroll for the next month.
Check App Store Connect / Google Play Console dashboard for a brief overview.
The best way to calculate Trials is to handle Apple/Google server2server notifications and build custom views.
Adapty shows you:
Get all this data for iOS and Android instant as soon as you install SDK.