Churned ARR is the Annual Recurring Revenue lost from a company's existing contracts that are no longer in effect. This could be due to reasons like non-renewal or cancellation of a contract within the contract period.
Suppose ABC Co. has an ARR of $100,000 and at the time of renewal, it decides to discontinue or not renew the contract. This causes the ARR to drop to $0. Thus, Churned ARR = $100,000.