The Borg designation for a Delta Quadrant civilisation whose ships and hundreds of thousands of people were assimilated in 2375 while the Borg Queen made Seven of Nine watch.
Species 10026 is known only by the number the Borg Collective gave it. Its people are humanoid and travel in a fleet of several dozen vessels when the Borg find them.
In the feature-length episode Dark Frontier, the Borg Queen has lured Seven of Nine back to the Collective and brings her aboard a cube to witness the assimilation of Species 10026 at first hand. Seven is ordered to help the drones overcome the aliens' defences and watches captives being led away for processing.
Moved by their terror, Seven quietly helps a handful of them reach a ship and slip away. The Queen notices at once, but lets the survivors go as a calculated indulgence, using the incident to probe the compassion Seven has learned aboard Voyager.