What is an unjust law?

First of all I have to define unjust. Unjust equals unfair, so when we talk about an unjust law we talk about a law with a lack of fairness. When we look back we find a lot of famous laws of which we can definatly say that they where unjust. For example the laws which were results of Hitler's opinion of the Jews. An other example of unjust laws would be the former laws against black people in America. But in my opinion unjust laws are also findable at this time. It is just depending for whom there are findable. In Germany the richer people have to pay a lot more taxes, so this law might be an unjust law for them but not for the poorer people. In some cases mostly everyone in the society would treat certain laws as unjust laws. It depends on everyone's own opinion whether a law is an unjust law.