Medicare

Medicare is a U.S. national health insurance program started in 1966 under the Social Security Administration (SSA), which is now administered by the Centers for Medicare and Medicaid Services (CMS). It primarily provides health insurance for Americans aged 65 and older, but also for younger people with SSA-determined disability status, and people with end stage renal disease and amyotrophic lateral sclerosis (ALS or Lou Gehrig's disease).

In 2018, Medicare provided health insurance for 59.9+ million individuals — 52+ million people aged 65 and older and about 8 million younger people. Medicare covers about half of healthcare costs of those enrolled. See here for more Medicare details.