Final answer:
Medicare is a health insurance program for three groups of people: individuals aged 65 and older, individuals who meet certain criteria for disability, and individuals with end-stage renal disease (ESRD).
Step-by-step explanation:
Medicare is a health insurance program that provides coverage for three groups of people. The first group includes individuals who are aged 65 and older. The second group consists of individuals who meet certain criteria for disability, regardless of their age. Lastly, Medicare also covers individuals with end-stage renal disease (ESRD), which is a condition where the kidneys no longer function properly.