Jem'Hadar battleship firing on the Atbar Prime base
Atbar Prime was the prime planet in the Atbar system, Alpha Quadrant. This base was in or near to Cardassian space.
During the Dominion War, this planet was host to a Cardassian Liberation Front base. 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 was 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.