Benzar was the homeworld of the Benzite civilization, and a significant member of the United Federation of Planets. Benzar's atmosphere differed somewhat from class M norms, such as that, before the 2370s, Benzites who were off-world required a breathing apparatus. (TNG: "Coming of Age", "A Matter Of Honor"; DS9: "The Ship")
During the Dominion War, Benzar had fallen to Dominion and Cardassian forces by 2374. However, the planet was liberated by the Romulan Star Empire later the same year, after it joined the war on the side of the Allies. Constable Odo expressed concerns that the Romulans would not give up control of Benzar even after the war ended, as their usual policy was to keep claimed territories. (DS9: "The Reckoning")
In 2399, the location of Benzar was labeled in a star chart that was in Fleet Admiral Kirsten Clancy's office at Starfleet Headquarters. This planet was in or near to Federation space. (PIC: "Maps and Legends")
This planet was only mentioned in dialogue.
Based on the star charts seen as the Enterprise-E raced back to Federation space after their first encounter with the Scimitar, it's likely that, by this point, Benzar had once again passed into Federation control, although this has yet to be confirmed in canon.
According to The Worlds of the Federation, Benzar was the third planet in the Gamma Xertia system. Its natives call it "Pheradon".