The Borg's primary ship type, a vast cube that can regenerate and adapt to weapons.
The Borg cube is the signature vessel of the Borg Collective, an enormous cube with no bridge, no decoration and no crew quarters beyond the alcoves where thousands of drones regenerate. The ship is decentralised, so damage to one section can be repaired while the rest keeps working, and its drones share the hive mind and adapt quickly to the weapons used against them.
Starfleet's first encounter came when Q hurled the Enterprise-D into distant space, where a cube carved a section out of the ship. A cube later invaded Federation space, assimilated Captain Picard as Locutus and wiped out the fleet gathered at Wolf 359. The Enterprise crew rescued Picard and used his link to the Collective to send the drones a command to sleep, after which the cube destroyed itself.
In 2373 another cube reached Earth and was destroyed by a Starfleet fleet, though it first launched a sphere into the past. In the Delta Quadrant, Voyager met many cubes and briefly allied with the Borg against Species 8472.