Approval rate is the percentage of charge attempts that are actually approved by the card's issuing bank, relative to the total number of attempts processed in a period. An approval rate of 70%, for example, means 3 out of every 10 charge attempts are declined.
In international sales, the approval rate tends to be more sensitive than in the domestic market, because the issuing bank is evaluating a transaction in a foreign currency, often without recognizing the cardholder's purchase pattern in that context.