A blacklist is a negative list created according to certain criteria (country of origin of the credit card or IP address). If you do not want to allow credit card payments from certain countries, you can have the corresponding country added to the blacklist.
Payments from countries that are not on this list are allowed.
The blacklist follows the approach that basically everything is forbidden that is explicitly entered in the list.
A whitelist is a positive list created according to certain criteria (country of origin of the credit card or IP address). If you want to allow credit card payments only from a defined list of countries, you can have the corresponding countries added on the whitelist. Payments from countries that are not on this list are blocked.
The whitelist thus follows the approach that basically everything is prohibited that is not explicitly entered in the list.