Define the term 'income inequality'

Income inequality is a statistical measure concerned with the spread of the distribution of income amongst the population of an economy.

It can be quantified through a variety of measures which condense the entire income distribution of a country into a single figure: varying from the range of incomes in a given population, the 90:10 ratio and, most notably, the Gini coefficient.

Focusing on the Gini coefficient, this is a measure which produces a figure between 0 and 1 for a given income distribution - the closer the figure is to 1, the more unequal the population.