Alpha Onias III was the uninhabited third planet of the Alpha Onias system. This system was located in the Onias sector, a region of space near the Romulan Neutral Zone. Although it was class M, Starfleet survey teams listed Alpha Onias III as barren and inhospitable with an atmosphere containing high, but non-toxic, levels of volcanic gases, including sulfur dioxide, methane, and hydrogen sulfide.
Barash, a humanoid child, was hidden in a cavern by his mother after their homeworld was attacked in the mid-24th century. The cavern was equipped with neural scanners that were able to transform matter into any form imagined, so that Barash could live in safety. (TNG: "Future Imperfect")
OH-nye-is was the pronunciation for Onias according to the script pronunciation guide.
The planet model for Alpha Onias III was first used for Ramatis III. ("Loud As A Whisper") It was used again for Gamma Hromi II. ("The Vengeance Factor")
According to the Star Trek: Star Charts, on page 61, the Alpha Onias system was located in or near to Romulan space, in the Beta Quadrant. Alpha Onias was a single star system. Primary was a class M star with a magnitude of +9.