What does this mean by accounts will be subject to a penalty when the account is beyond 10 days overdue at the rate of 2 percent a month?

What does this mean by accounts will be subject to a penalty when the account is beyond 10 days overdue at the rate of 2 percent a month?
There is a due date on the payment, if you miss that, the charge added to your balance is 2 percent per month till you get current.