Accident-only coverage is an add-on to your regular health insurance and pays a specific amount for certain types of health care that's needed after an accident, car crash, or fire. Its role is to lower how much you would have to spend if you have an accident.
Accident-only coverage does not cover health care if you get sick. For instance, if you find out you have cancer, this kind of plan will not cover your health care expenses. It only covers some specific issues caused by an accident.