See: Medicare.
"Medicare advantage"...what you might hear an announcer say in a close tennis match between Medicare and Medicaid.
Medicare offers basic health insurance for elderly and disabled Americans. The coverage it provides is adequate, but not all-encompassing. Because there are holes in the coverage, recipients can choose to expand their services with add-ons. These programs fall under the general category of “Medicare Advantage Plans.”
It's like the government provides the Medicare hamburger for free...but you can choose to pay extra for condiments.
Except, of course, that the mustard and ketchup in this case are...pretty important. Prescription drugs, dental, hearing...that kind of thing.