Final answer:
Churn rate refers to the rate at which customers leave a product or service. It is an important metric for businesses to understand and manage.
Step-by-step explanation:
The correct answer to the question is d. Churn rate refers to the rate at which customers leave a product or service. It measures customer attrition and is an important metric for businesses to understand and manage. By calculating churn rate, businesses can identify potential issues and take steps to improve customer retention.