Private insurance that covers Medicare deductibles.
What’s Medicare Supplement Insurance (Medigap)?, Medicare.gov:
Medigap is Medicare Supplement Insurance that helps fill “gaps” in Original Medicare and is sold by private companies. Original Medicare pays for much, but not all, of the cost for covered health care services and supplies. A Medicare Supplement Insurance (Medigap) policy can help pay some of the remaining health care costs, like:
Note: Medigap plans sold to people new to Medicare can no longer cover the Part B deductible. . . .