Educational attainment means educational achievement. The authors compare educational achievement in different countries, emphasizing the connection between inequality and poor educational attainment.

The Gini Coefficient is a method used to measure a society’s inequality. If a society was extremely unequal, its label would be 1, while a perfectly equal society would be a 0, so the lower the score, the more financially equal the society. The authors use the Gini Coefficient to analyze the inequality rates in different US states because the US Census Bureau and most economists rely on this method.

Income inequality refers to the gap between people’s incomes. In The Spirit Level, Wilkinson and Pickett analyze incomes after taxation to investigate how much income variation there is between different nations.