Malum in se is a Latin term that means "wrong in itself."
In the context of the law, it refers to acts of wrongdoing that are blatantly against the standards of a civilized society. For example, rape, murder, arson and armed robbery are all examples of crimes that are considered malum in se.
Crimes that qualify as malum in se are an alternative to crimes that are designated as "malum prohibitum." Malum prohibitum crimes are crimes that are only classified as crimes due to particular statutes in a society, such as driving above the speed limit. But unlike rape or murder, there is nothing inherently evil about driving at 75 miles per hour, for example. Malum in se crimes can be punished much more severely that malum prohibitum crimes.