What is churn?
Churn is the share of paying subscribers who cancel in a period — per month for monthly plans, per year for yearly ones.
Churn decides how long an average subscriber stays: one divided by churn. At 10% a month the average subscriber pays for ten months; at 5%, twenty.
Churn is usually highest in the first months and falls for those who stay. Yearly plans turn it into one decision a year, which is a large part of why apps push them.