What does "inequality" mean?

Inequality: Unevenness; want of levelness; the alternate rising and falling of a surface; as, the inequalities of the surface of the earth, or of a marble slab, etc. The country is cut into so many hills and inequalities as renders it defensible. Addison.

Additional senses

  1. 2.Variableness; changeableness; inconstancy; lack of smoothness or equability; deviation; unsteadiness, as of the weather, feelings, etc. Inequality of air is ever an enemy to health. Bacon.
  2. 3.Disproportion to any office or purpose; inadequacy; competency; as, the inequality of terrestrial things to the wants of a rational soul. South.
  3. 4.(Alg.) An expression consisting of two unequal quantities, with the sign of inequality (> or <) between them; as, the inequality 2 < 3, or 4 > 1.
  4. 5.(Astron.) An irregularity, or a deviation, in the motion of a planet or satellite from its uniform mean motion; the amount of such deviation.

Sources