The share of customers who stop paying or stop using the product in a given period — the leak that every acquisition effort is working against.
At high churn, growth is just replacement. It also quietly caps valuation, because lifetime value falls with every point of monthly churn.
We make churn observable by cohort and by plan, and we look at what people did in their first week before they left — most cancellations are decided during onboarding, not at the cancel button.