What is Unjust?

Legal Definition
That which is done against the perfect rights of another; that which is against the established law; that which is opposed to a law which is the test of right and wrong. 1 Toull. tit. prel. n. 5; Aust. Jur. 276, n.; Hein. Lec. El. §1080.
-- Bouviers Law Dictionary
Legal Definition
Contrary to right and justice or to the enjoyment of his rights by another or to the standards of conduct furnished by the laws.
-- Black's Law Dictionary