Erabus Prime was the prime planet in its star system. This system was located in the Gamma Quadrant.

Erabus Prime was visited by Vash while in the company of Q. Vash was bitten by an insect on the planet that would have caused an allergic reaction to appear all over her body, were it not for Q's intervention. (DS9: "Q-Less")

This planet was only mentioned in dialogue.
According to and the script pronunciation guide, the pronunciation for Erabus was "AIR-uh-bus". [1] [2]
According to Star Trek: Star Charts (p. 75), this was a quaternary system with a pair of G-class stars and a pair of M-class stars.