When used in a business context.
noun:
Churn is used when referring to 'churn rate'.
Churn rate or
churn, is the percentage of people that stop using or subscribing to a service within a certain time frame. For a business to be profitable, its
growth rate must exceed its churn. As well as customer churn, there is revenue churn.
verb: These customers that have left have 'churned'.