A system that taxes everyone at the same rate, regardless of their income bracket.
Supporters of a flat tax argue that it gives people incentive to earn more, because they wouldn't be penalized by graduating to a higher tax bracket (as they would in a progressive-rate system).
Roth IRA: Back To Basics - Be sure to consider the tax benefits of the Roth IRA--but also the eligibility requirements to fund one and take tax-free distributions.