It's insurance to cover the difference between the appraised value of your car and the amount you still owe on the loan for the car. For example, if you owe $10,000 on your car and it's currently worth, say, $8,000, if you were to get in an accident totalling your car, regular insurance would only reimburse you $8,000 and you'd still owe an additional $2,000 to pay off the loan.