Nothing. Medigap and Medicare Supplement Insurance mean the same thing. Two different terms that describe the same product. A Medigap Plan (or Medicare Supplement Insurance) is designed to cover what original Medicare Part A & B does not. Medicare along with a Medigap Plan/Medicare Supplement is great health insurance. There is no network so you can go to any doctor or hospital you want. If they take Medicare they will take the supplement.
I would be happy to answer any other questions you have.
I would be happy to answer any other questions you have.