Quintiles are divisions of U.S. households into five equal segments.
In studies characterizing income by quintile, the top 20% of income-earning households placed in the top quintile, the bottom 20% of income-earning households placed in the bottom quintile, and others ranked between. Each income quintile consists of one-fifth (20%) of the population being studied. The U.S. Census Bureau reports income inequality yearly as the share of all income obtained by each income quintile. In a hypothetical nation of perfect income equality, each income quintile would obtain a 20% share of income. In a hypothetical nation of perfect income inequality, the top quintile would obtain 100% of all income and the other quintiles would obtain 0% of income. The income quintiles for any actual nation lies somewhere between these extremes.
Wealth is also characterized by quintile. See Ed Wolff’s Recent Trends in Household Wealth for relatively recent data on wealth inequality characterized by quintile.