A chargeback is a dispute around a card transaction.
It's the process of debiting the merchant payment account to credit the cardholder account following a claim. A chargeback is initiated by the cardholder bank and it is the bank duty to determine if the claim is reasonable or not.
This is not a refund* and is initiated by the cardholder. It's the bank's duty to determine whether such a request was reasonable or not. A chargeback is captured* during the bank reconciliation.
*A refund is initiated by the merchant to return the transaction to the end-user.
A chargeback is taken into account in case of (non exhaustive):
- fraudster card transaction
- duplicate payment
- stolen card...
You can see the chargebacks with API request (technical information here).