a system in the US by which people who have Medicaid pay money to a company so that they can receive additional medical care and services that they need
My mom has to pay high premiums every month for Medigap to cover prescription drugs.
From Longman Business Dictionary
MedigapMed·i·gap /ˈmedigæp/ noun [uncountableU]
a type of private medical insurance in the US that covers costs not paid by Medicare
Congress has now enacted legislation to standardize Medigap policies.