Malum In Se

Evil in itself.

An offence malum in se is one which is naturally evil, as murder, theft, and the like; offences at common law are generally mala in sese.

An offence malum prohibitum, on the contrary, is not naturally an evil, but becomes so in consequence of its being forbidden; as playing at games, which being innocent before, have become unlawful in consequence of being forbidden.
   

This entry contains material from Bouvier's Legal Dictionary, a work published in the 1850's.