Yadera II was the second planet in an unspecified system located in the Gamma Quadrant.
Yadera II was named after Yadera Prime, homeworld of the Yaderans. It became the refugee Rurigan's new home after the Dominion invaded his homeworld of Yadera Prime in 2340. With the help of a hologenerator, he created sentient holographic lifeforms on the planet. (DS9: "Shadowplay")
The planet's name is not from the episode. Rather, it is from StarTrek.com and the Star Trek Encyclopedia (3rd ed., p. 568).
According to the script, the pronunciation for Yadera was "yah-DER-ah".