Cardassia V was the inhabited fifth planet in the Cardassian system, in the Alpha Quadrant. The planet was affiliated with the Cardassian Union.
In 2370, Kono was wanted there for stealing bone carvings from a museum. (DS9: "Shadowplay")
In 2375, the location of Cardassia was labeled on a tactical map that was displayed in the wardroom of Deep Space 9. (DS9: "When It Rains...", okudagram)
Background information Edit
This planet was only mentioned in dialogue.
"car-DASS-ee-uh" was the pronunciation for this planet's name from the script pronunciation guide for "Tribunal". 
According to a stellar cartography map, seen in the Star Trek: Deep Space Nine Technical Manual, the Cardassian system was located in the Bajor sector. 
According to Star Trek: Star Charts (pp. 37, 43, 46), Cardassia V (Cardassia Minor) was classified as a M-class world. The primary of Cardassia V was a K-class star.