(Automated Clearing House) A system of the U.S. Federal Reserve Bank that provides electronic funds transfer (EFT) between banks. It is used for all kinds of fund transfer transactions, including direct deposit of paychecks and monthly debits for routine payments to vendors. The ACH is separate and distinct from the various bank card networks that process credit card transactions. ACH operations are done in a batch mode, which can take up to 72 hours before the money is actually transmitted. A return notification is sent if there are insufficient funds in the account.