A concealed chamber at the heart of a Borg cube, reserved for the Borg Queen, containing an emergency spatial trajector and the controls from which the vessel can be commanded.
The queencell is a shielded room that can only be found and opened by those the cube recognises. It gives a Queen a place of safety when she is aboard and holds technologies the Collective has assimilated for her use.
It is seen in the first season of Star Trek: Picard aboard the Artifact, the disabled cube in Romulan hands. In The Impossible Box, Hugh leads Picard and Soji there and uses its Sikarian spatial trajector to send them to safety on Nepenthe.
In Broken Pieces, Seven of Nine returns to the queencell and links herself to the cube, briefly becoming the centre of a small collective in order to rouse the surviving drones against the Romulans.