Jem'Hadar battleship firing on the Atbar Prime base
Atbar Prime was the prime planet in its star system. During the Dominion War, this planet was the location for a base of the Cardassian Liberation Front. The base was one of eighteen destroyed by Dominion and Breen forces in late 2375. (DS9: "The Dogs of War")
This planet's quadrant of origin is inferred based on the position of the Cardassian Union as seen in the star chart appearing in the Star Trek: Picard episode "Maps and Legends".
"AT-bar" was the pronunciation for this planet's name from the script pronunciation guide.
According to Star Trek: Star Charts (p. 46) and Stellar Cartography: The Starfleet Reference Library ("Stellar Cartography", p. 18; "Federation Historical Highlights, 2161-2385"), the Atbar system was located in the Alpha Quadrant. This system was a binary with a pair of G-class stars. According to a map of the Cardassian Union – prepared by an anonymous astrography clerk, from the Cardassian Central Archives, in 2364 – Atbar was identified as a Cardassian system.