What is the difference between transaction.chargeback.* and transaction.refund.* events?

Refund events occur when the merchant performs a voluntary repayment to a cardholder (e.g. the cardholder didn't receive goods/services and is compensated by the merchant), while chargeback events occur when the bank reverses a transaction (e.g. a cardholder disputes a transaction with a merchant with the bank, and the funds are returned).