Defera is a class M planet in the Defera system of the Orellius sector block, between the territories of the Cardassian Union and the Breen Confederacy. It is the homeworld of the Deferi species. (Star Trek Online)
Defera has no moons, but is ringed by an asteroid and debris field.
In the early 25th century, Defera faced invasion from both the Breen and the Borg Collective. The USS Skyfall was lost in a confrontation with the Borg near Defera. (Star Trek: Sons of Liberty: "For I Dipt Into the Future...")