After an insurance company has paid benefits to a person injured in an accident, subrogation refers to the process of the insurance company later seeking reimbursement from the person legally responsible for causing the accident. 
Under Pennsylvania law, if you are injured in an auto accident, your auto insurance company has no right of subrogation.  However, if you exceed the medical coverage provided by your auto insurance, and some of your bills are paid by your private health insurance plan, that private health insurance company may have a right of subrogation.  That means that if you are able to recover money damages from the responsible driver, your private health insurance company may have a right to some of the money you recover from the responsible driver, effectively reducing your recovery.
Whether your private health insurance company has a right of subrogation depends on the type of plan you have.  If you have been injured in an accident, contact me here to discuss your legal rights, and how subrogation may or may not affect your recovery.