Zetli was a planet located somewhere in the space of the galaxy's Alpha or Beta Quadrants, in orbit of the Zetli system.
History and specifics[]
In the 24th century, this location was known to be inhabited and was in or near the Federation.
When discussing potential career choices with her mother in the 2350s decade, Deanna Troi stated that her options were her own, even if she wanted to paint herself blue and become a naked dancing girl in the Zetli system. Some time later, Lwaxana Troi responded that she wouldn't want Deanna to do that because it was so cold on the planet Zetli. (TNG novel: Imzadi)