Churn rate is the percentage of customers (or revenue) lost over a defined period, typically expressed as an annualised figure. Churn can be measured in customer terms (number of customers lost) or revenue terms (value of revenue lost), and the two figures often differ where small customers churn at higher rates than large ones.
Check whether churn measures customers or revenue, and whether the calculation is gross or net. Use a consistent period and definition when comparing results.