Churn Definition

A churn definition is the rule that decides when a user counts as lost: which action stops, for how long, and within which population.

There are two families. In a contractual product the definition is anchored to an event, a cancellation or a non-renewal at the end of a term, and the churn date is known exactly. In a non-contractual product no such event exists, so the definition becomes an inactivity threshold: no qualifying action for a set number of days. Choosing that number is a trade-off. A short window labels seasonal users as churned too early and inflates the figure, while a long window is more accurate but reports the loss after the point where anything can be done about it. The threshold should be derived from the product's own distribution of return times, the point beyond which almost nobody comes back, not copied from another product. Every churn number is meaningful only next to its definition, so changing the rule breaks comparability with the older series.