The minimum amount of discount fees charged by a processing bank in a given month. If account activity does not generate the monthly minimum, the merchant pays the difference. Example: Most banks in the US charge a $25.00 monthly minimum. If you have a $100.00 sale, and you are paying a 2.5% discount rate, the bank collects $2.50 for their services. The $2.50 is deducted from your monthly minimum, and if that sale were your *only* sale of the month, you would be billed the remainder of $22.50 by the processing bank.