Federal Income Tax: A tax levied by the United States Internal Revenue Service (IRS) on the annual earnings of individuals, corporations, trusts, and other legal entities.
Constitutional Amendment: A modification or addition to a constitution. In U.S., it requires approval by two-thirds majority in both houses of Congress and ratification by three-fourths of states.
Progressive Tax: A tax that takes a larger percentage from high-income earners than it does from low-income individuals. The 16th amendment made progressive taxation possible at federal level.