When is my car a "total loss"?
A car is considered a total loss or "totaled" when the cost of repairing the car is more than the car is worth. In that case, the insurance company only pays you the car's fair market value, and will not pay to have the car repaired. In effect, the accident results in the "sale" of your car. In other words, if you were to advertise your car for sale, what would a prospective buyer reasonably pay you for your car.
The car's FMV is determined by comparing it with the current sale price of similar year, make and model cars in the area. Often, insurance adjusters will look at the NADA blue book which is available at your local public library.