Zetar was a formerly inhabited planet. This was the homeworld for the Zetarians, an extinct humanoid species.
The planet was subject to a massive cataclysmic event which destroyed all corporeal life there. When all life died, only a hundred or so of the resident civilization lived on as a pattern of lights and non-corporeal energy. (TOS: "The Lights of Zetar").
According to Star Trek: Star Charts ("United Federation of Planets") and Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), there was a star system named Zetar, in which this planet might possibly have been located, in the Alpha Quadrant. The system's primary was a M-class star.
External link 
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- Zetar at Memory Beta, the wiki for licensed Star Trek works
