Accident-only coverage is not health insurance. It is supplemental incurance that pays a specific amount for certain types of health care that's needed after an accident, car crash, or fire. It’s sold separately from health insurance and often from companies that specialize in accident, disability, or life insurance. 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.