The Republic staging grounds was a large facility on Coruscant that was used by the Galactic Republic to prepare large cruisers, most notably Venator-class Star Destroyers, for travel. It was located nearby the Republic Military Base.
Behind the Scenes
Three scenes of "Duchess of Mandalore" were to take place at the staging area depicting Anakin Skywalker preparing the 501st Legion to occupy Mandalore. These scenes were fully animated, but were cut from the final episode either for the sake of time or other reasons.