What is Medigap or Medicare supplement insurance?
People who have Medicare should educate themselves to understand their supplemental insurance options called Medigap (also called “Medicare Supplement Insurance”) policies. The U.S. Government Medicare office defines a Medigap policy as a type of private insurance that helps you pay for some of the costs that Original Medicare doesn’t cover.
The official 2012 government guide from the Centers for Medicare and Medicaid Services,
Choosing a Medigap Policy:
A Guide to Health Insurance for People with Medicare
explains medicare supplement or Medigap insurance:
A brief look at Medicare
This guide helps people with Medicare understand Medigap (also called “Medicare Supplement Insurance”) policies.
A Medigap policy is health insurance sold by private insurance companies to fill gaps in Original Medicare coverage. Medigap policies can help pay your share (coinsurance, copayments, or deductibles) of the costs of Medicare-covered services. Some Medigap policies also cover certain benefits Original Medicare doesn’t cover. Medigap policies don’t cover your share of the costs under other types of health coverage, including Medicare Advantage Plans, stand-alone Medicare Prescription Drug Plans, employer/union group health coverage, Medicaid, Department of Veterans Affairs (VA) benefits, or TRICARE. Insurance companies generally can’t sell you a Medigap policy if you have coverage through Medicaid or a Medicare Advantage Plan.

Click the above image to link to the Official 2012 Medicare Guide to Choosing a Medigap Policy - a guide to health insurance for people with Medicare.