An assimilation chamber of a Borg cube
An assimilation chamber was a section on a Borg vessel where the assimilation of an individual or group of individuals into the Borg Collective was performed. (VOY: "Dark Frontier")
In 2376, USS Voyager crewmembers Chakotay, Tom Paris, and Neelix were held captive in an assimilation chamber of a Borg cube, by a group of adolescent drones who were the sole survivors of a deadly pathogen which had killed the rest of the Borg on the ship. (VOY: "Collective")