Thalos VI was the sixth planet in its system. The Ferengi Gaila was arrested there in 2374 for vagrancy. (DS9: "The Magnificent Ferengi")

This planet was only mentioned in dialogue.
Gaila was subsequently detained on a Starfleet station, suggesting that the planet was under Federation juristiction.
According to Star Trek: Star Charts ("United Federation of Planets I") and Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), the Thalos system was located in the Alpha Quadrant. This was a trinary system with a M-class star, a G-class star, and a K-class star.

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