Malum in se is Latin and means wrong or evil in itself. There is a universal understanding across countries and cultures that actions are evil in them self. Examples of such actions are:
Malum in see must be present for a society to exist.
Malum prohibitum is the opposite of malum in see. That means an act is not illegal because they are basically bad, but because they are because of law. The law may be different across borders, such as child marriage.
Another example is that they drive on the left side of England while in USA we drive on the right side of the road. It is not because it is immoral to drive on the left, but there is a law due to road safety.