Churn
Churn is the percentage of subscribers who cancel in a given period. In a membership it is the metric that decides whether the business grows or merely replaces what it loses each month.
At 10% monthly churn, half your base disappears in under a year and all commercial effort goes into plugging the hole.
The most common cause is not price but disuse: people who have not logged in for weeks cancel. Activity signals predict cancellations far better than any satisfaction survey.