The U.S. federal income tax system is 'progressive,' which means what?

Progressive taxation means different portions of income are taxed at different rates. For 2025, income up to $11,925 (single filer) is taxed at 10%, income from $11,925 to $48,475 at 12%, and so on. Moving into a higher tax bracket does NOT mean your entire income is taxed at the higher rate, only the income within that bracket.