inequality

Concise Oxford English Dictionary © 2008 Oxford University Press:
inequality/ɪnɪˈkwɒləti/

▶noun (pl. inequalities)

• 1 lack of equality.

• 2 Mathematics a symbolic expression of the fact that two quantities are not equal, employing a sign such as ≠ ‘not equal to’, > ‘greater than’, or < ‘less than’.

• 3 archaic lack of smoothness or regularity in a surface.