What does 'average available balance' mean?

Let's say that you have a checking account with a debit card. Your balance is the amount of money in the account. However, the available balance may be lower. When you deposit a check, the bank can place a hold on those funds until the deposited check clears. The amount of the check is added to your balanceimmediately, but is not added to your available balanceuntil the hold clears. Also, when you use your debit card, the merchant may place a hold on some amount of money when they initially authorize the charge. (For example, if you pay for gas at the pump, the gas station may pre-authorize a set amount such as $75.00, even if you end up only buying $30 worth of gas. Also, restaurants will typically pre-authorize an amount somewhat higher than your bill, to allow you to add a tip to the amount charged to your card.) Those merchant holds from your debit card will also temporarily reduce your available balance, until the hold expires or is cleared.

The average available balance is simply the average of the daily available balances for a month, or whatever period is covered by your statement.