What is a Credit (Reversal / Refund)?
A credit (reversal/refund) is a merchant’s reversal of an authorized transaction (sale) that has been settled. It's supported by the card issuer, a reversal will immediately ‘undo’ an authorization and return it to the open-to-buy balance on a Cardholder’s account.
Electronic Merchant Systems Payment Processing Glossary :
Defining key payment processing and merchant services industry terms to help business owners make better decisions.