Alpha Onias III was the uninhabited third planet of the Alpha Onias system, in the Beta Quadrant. 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"; DIS: "Magic to Make the Sanest Man Go Mad")