Posted balance and available balance difference?

My checking account says that I have a posted balance of $250, however it says I have an available balance of $240.69. What exactly does this mean and why did it happen? I recently charged something to my debit card on Amazon, and in the "view holds" area it shows a payment to amazon for $9.31, which would explain the lower available balance, however what i bout on amazon cost me around sixty dollars, not ten. What's going on?|||It sounds strange, but that's why banks have a "pending" or "hold" status for transactions. They've received some information, but not enough to confirm it's finalized. Assume the full amount will process in the next few days and your balance is $200 to avoid any over-the-limit fees from the bank.