What do you call a moon of a moon?

If a satellite orbits a planet, it is called a moon. But if a satellite orbits a moon, what is it called? Clearly, Newtonian physics permits such orbital behavior. In fact, in our exploration of our own moon, we put artificial satellites in orbit around it. So if we can do it, nature can too. In the vastness of the Universe, there must be instances of such orbital relationships. But is there a unique name for the moon of a moon?