A proportional or flat tax system assesses the same tax rate on everyone regardless of income or wealth. This system is meant to create equality between marginal tax rates and average tax rates paid.
Other examples of proportional taxes include per capita taxes, gross receipts taxes, and occupational taxes.
Proponents of proportional taxes believe they stimulate the economy by encouraging people to work more because there is no tax penalty for earning more. They also believe that businesses are likely to spend and invest more under a flat tax system, putting more dollars into the economy.