Mariah IV was the inhabited fourth planet in its star system.

Along with Fahleena III and Ultima Thule, Mariah IV was a stop on a route formerly taken by Valerian traders supplying weapons-grade dolamide to the Cardassians.

The Valerian transport ship Sherval Das visited this planet in 2369. (DS9: "Dramatis Personae")

This planet was only mentioned in dialogue.
According to the script and, the pronunciation for Mariah was "muh-RYE-uh". Futhermore, this website located the primary Mariah in the Bajor-Cardassia region of the Alpha Quadrant.
According to Star Trek: Star Charts (p. 46) and Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), the Mariah system was located in the Alpha Quadrant. This was a binary system with a pair of F-class stars.