Original Medicare includes Medicare Part A (Hospital Insurance) and Part B (Medical Insurance). If you want drug coverage, you can join a separate Medicare drug plan (Part D). Medicare Advantage is an “all in one” alternative to Original Medicare. These “bundled” plans offer extra benefits Original Medicare doesn’t cover–like vision, hearing, dental, and more.
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.
If you enrolled in a Medicare Advantage Plan during your Initial Enrollment Period, you can change to another Medicare Advantage Plan (with or without drug coverage) or go back to Original Medicare (with or without a separate Medicare drug plan) within the first 3 months you have Medicare.