Final answer:
Medicaid is a joint health insurance program that provides medical insurance for low-income people. 31 states and the District of Columbia have expanded their Medicaid program to include more low and moderate-income citizens.
Step-by-step explanation:
Medicaid is a joint health insurance program between states and the federal government that provides medical insurance for certain low-income people, including those below the poverty line, with a focus on families with children, the elderly, and the disabled. Currently, 31 states and the District of Columbia have expanded their Medicaid program as a part of the Affordable Care Act (Obamacare). By expanding their Medicaid eligibility standards, these states have granted public medical insurance to many more low and moderate-income citizens.