What does it mean for a patient to have dual insurance coverage?

This refers to the case in which a patient is insured by more than one insurance plan. For example, a Medicare patient is generally covered for 80% of charges for a physician visit. In this case , he or she would usually be responsible for the remaining 20% of charges. However, if he or she has dual insurance coverage and is also covered by a supplemental plan. Medicare plus, this secondary plan would generally pay the amount not covered by the patient's primary insurance plan, Medicare.