Gammma Hromi was a planetary system in the Hromi Cluster, in the Beta Quadrant. One of its planets was Gamma Hromi II. It was located near Starbase 24, Ramatis, and the Federation border with the Klingon Empire.
In 2256, this system's location was labeled on the star chart "Alpha/Beta Quadrant Overview" in the ready room aboard the USS Discovery. (TNG: "The Vengeance Factor"; DIS: "Magic to Make the Sanest Man Go Mad")
In 2257, during the Federation-Klingon War, this star's system was occupied by the Klingons. (DIS: "The War Without, The War Within")
In 2259, the location of this system was labeled on a stellar cartography chart that was seen on the USS Enterprise's ready room viewscreen. This system's symbol had a blue color, indicating that it was affiliated with the United Federation of Planets. (SNW: "Strange New Worlds", "Children of the Comet", "Spock Amok")
The system's location was labeled in a Federation star chart that was in Fleet Admiral Kirsten Clancy's office at Starfleet Headquarters in 2399 and on the bridge of the USS Titan-A in 2401. The Gamma Hromi system was in or near to Klingon space. (PIC: "Maps and Legends", "The Next Generation", "Disengage")
This star was only mentioned in writing.
According to Star Trek: Star Charts (pp. 61, 66) and Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), the Gamma Hromi system was a quaternary star system with a G-class star, a pair of K-class stars, and a M-class star.