The Monac shipyards were Cardassian-Dominion shipyards located above Monac IV, near the Monac star. They were a crucial production facility for the Dominion effort to retake the Chin'toka system.
Among the vessels constructed there included Galor-class warships, Jem'Hadar battle cruisers and Jem'Hadar fighters.
In 2375, a Klingon fleet attacked the shipyards but failed to destroy them, suffering losses of over thirty percent in the process. Shortly after, General Martok and Lieutenant Commander Worf successfully destroyed the shipyards using just the IKS Rotarran, by triggering a solar plasma ejection from a magnetic instability on the Monac sun. (DS9: "Image in the Sand", "Shadows and Symbols")
The Monac shipyards were designed by John Eaves and named after DS9's special effects supervisor Gary Monak. (Star Trek: Deep Space Nine Companion, p. 598)
According to Star Trek: Star Charts (p. 46), the Monac shipyards were located in the Alpha Quadrant.