A Casino Credit line is tied to the bank account of your choosing. Each time you are issued a marker (counter check), a due date is assigned. Any outstanding markers (counter checks) not paid by its due date will be electronically presented to your bank for payment.
Casino credit is primarily for high rollers those who bet big, lose big, and, like the abovementioned whale, pay off big for the host casino, even when they get a markdown. But it's also for those who'd rather play against a line of credit than carry cash, or who exceed the daily ATM limits imposed by their banks.