Arrow Impossibility Theorem: A mathematical theorem that holds that no system of voting can be devised that will consistently represent the underlying preferences of voters.

Average Tax Rate: The average percentage of income paid in taxes among a population. 

Excess Burden: A measure of the efficiency loss to the economy that results from a tax having reduced the quantity of a good produced; also known as the deadweight loss.

Lorenz Curve: A curve that shows the distribution of income by arraying incomes from lowest to highest on the horizontal axis and indicating the cumulative fraction of income earned by each fraction of households on the vertical axis.

Marginal Tax Rate: The fraction of each additional dollar of income that must be paid in taxes.

Median Voter Theorem: The proposition that the outcome of a majority vote is likely to represent the preferences of the voter who is in the political middle. 

Poverty Line: A level of annual income equal to three times the amount of money necessary to purchase the minimum quantity of food required for adequate nutrition

Poverty Rate: The percentage of the population that is poor according to the federal government’s definition. 

Progressive Tax: A tax for which people with lower incomes pay a lower percentage of their income in tax than do people with higher incomes

Public Choice Model: A model that applies economic analysis to government decision making. 

Regressive Tax: A tax for which people with lower incomes pay a higher percentage of their income in tax than do people with higher incomes.

Rent Seeking: Attempts by individuals and firms to use government action to make themselves better off at the expense of others.

Tax Incidence: The actual division of the burden of a tax between buyers and sellers in a market.

Voting Paradox: The failure of majority voting to always result in consistent choices.