Just like in long-term health insurance policies, short-term ones will not cover pre-existing conditions. So if you have been diagnosed with a medical condition before applying for a short-term or temporary insurance policy, it could not be used to cover costs that may arise from medication of your pre-existing medical condition. This is just one of the similarities between these types of health insurance policies.
Short-term insurance policies as its name suggest is a form of policy that will last for a short period of time and to be more exact this can lasts from 6 to 12 months. There are even shorter policies which could run for up to 30 days only.
A major difference between short term and long term health insurance policies is of course the time. But apart from that, it will not cover preventive care like physical exams. But it is designed to cover serious health conditions.