Acquirer, Acquiring Bank, Acquiring Institution
The financial institution supplying the merchant with means to accept credit cards for payments. The financial institution will charge the merchant a fee for providing these services.

ACH
Automated Clearing House - Allows for the exchange and settlement of electronic payments between financial institutions.

API
Application Programming Interface - An interface allowing integration with virtually any programmable software package or platform.

AVS
Address Verification Service - Typically used for mail order/telephone order transactions, an AVS response is given to indicate the level of accuracy of a given address based on the billing address of the customer's credit card.

Authorization
A transaction verifying the availability of funds in a cardholder's account to make the purchase (usually identified by an Approval Code).

Auto Close
The feature allowing some gateways and terminals to automatically batch transactions daily without them being initialized by the merchant.

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