What is National Health Insurance?

Legal Definition
National health insurance (NHI) – sometimes called statutory health insurance (SHI) – is a legally enforced scheme of health insurance that insures a national population against the costs of health care. It may be administered by the public sector, the private sector, or a combination of both. Funding mechanisms vary with the particular program and country. National or Statutory health insurance does not equate to government-run or government-financed health care, but is usually established by national legislation. In some countries, such as Australia's Medicare system or the UK's National Health Service, contributions to the system are made via general taxation and therefore are not optional even though use of the health scheme it finances is. In practice, of course, most people paying for NHI will join the insurance scheme. Where the NHI scheme involves a choice of multiple insurance funds, the rates of contributions may vary and the person has to choose which insurance fund to belong to.
-- Wikipedia
Legal Definition
A federal government's insurance benefits system established to cover all or almost all national citizens. The United States is developing such a program. Tax money funds these systems entirely or partially.