A more thorough explanation:

Definition: Contrary to justice; not just.

Example: It is unjust to punish someone for a crime they did not commit.

Explanation: The example illustrates the definition of unjust by showing that punishing someone for a crime they did not commit goes against the principles of justice. Justice requires that punishment be given only to those who are guilty of a crime, and punishing an innocent person is therefore unjust.