A “Medicare Supplement Insurance” policy (also called Medigap) is private health insurance that’s designed to supplement Original Medicare. This means it helps pay some of the health care costs that Original Medicare doesn’t cover (like copayments, coinsurance, and deductibles). These are “gaps” in Medicare Coverage. If you have Original Medicare policy, Medicare will pay its share of the medicare-approved amounts for covered health care costs. Then your Medigap policy pays its share.