This is the SaaS metric with most variations of them all.
Churn rate can be calculated for Customers/Accounts, Subscriptions, Users and MRR.
In addition to that there are net and regular (non-net) churn rates. The net churn rate is calculated from the whole customer base, while the regular churn rate is calculated from customers who can actually churn. Different variations are used for different purposes.
On top of that, businesses may use their own custom definitions for active customers. This means that you must be careful when comparing your churn rate to others.
Only non-SaaS businesses calculate Revenue Churn from non-normalized revenue and they use different formulas, SaaSes use MRR Churn instead.
FirstOfficer shows Net MRR Churn, Subscription Churn and MRR Churn. If your customers each have just one subscription, Subscription Churn is the same as Customer/User Churn.
Details, usage and formulas: Customer Churn Rate
Be sure to check out our awesome Churn guide.