Customer churn is a short version of ‘customer churn rate’, or ‘customer attrition rate’, and it measures the percentage of customers who stop buying from their existing supplier in a given period. Customer Retention Rate measures the same characteristic by measuring retained rather than lost customers.
These metrics are especially important in market segments dominated by subscription sales. Customer churn – the percentage of customers lost – is usually analyzed into those customers lost to competitors, and those who simply stop using a service.