Maxia Zeta III was the uninhabited third planet of the Maxia Zeta system. Like the fourth planet, this planet was located in the habitable zone of its star, and was therefore a candidate for terraforming. (TNG: "The Battle", display graphic)

This planet was only mentioned in writing.
According to Star Trek: Star Charts ("United Federation of Planets I") and Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), the Maxia Zeta system was located in the Alpha Quadrant.