Unicomplex

From Memory Alpha, the free Star Trek reference

The Unicomplex was a vast Borg complex located within Borg space in the Delta Quadrant. It was composed of thousands of connected structures and hubs spanning at least 600km that housed hundreds of Borg ships and trillions of drones. (VOY: "Dark Frontier")

It was considered by the independent drones to be the home of the Borg Queen. (VOY: "Unimatrix Zero")

The Unicomplex was destroyed in 2378 after the Borg Queen assimilated a neurolytic pathogen from the future Admiral Kathryn Janeway, who had traveled back in time to bring the USS Voyager home. The Queen activated a self-destruct order in the Unicomplex to prevent the pathogen from spreading, but it had already spread through most of the Collective by the time the Queen acted. (VOY: "Endgame")

It is unclear whether there is more than one Unicomplex. The Borg Drone Axum suggested that the independent drones attack the "Primary Unicomplex" implying that there are other, smaller unicomplexes. (VOY: "Unimatrix Zero, Part II")