A flat tax reflects a proportional tax system.
In a proportional tax system, the tax rate remains constant across all income levels. This means that all taxpayers, regardless of their income, are taxed at the same percentage rate. In a flat tax system, the tax rate is also the same for all taxpayers, which makes it a type of proportional tax.
Some proponents of a flat tax argue that it simplifies the tax code and makes it easier to understand and comply with, while others criticize it for potentially increasing income inequality and benefiting the wealthy at the expense of the poor.