Medicare Supplement insurance plans, also called Medigap are health insurance policies that help pay some of the health care costs that Original Medicare doesn’t cover. When you buy a Medicare Supplement insurance plan, you are still enrolled in Original Medicare, Part A and Part B. Original Medicare covers certain healthcare services, while the Medigap plan helps cover certain cost-sharing expenses required by Original Medicare, such as copayments or deductibles. You can apply for Medicare Supplement Insurance plans through private Medicare-approved insurance companies.