The Tainted are human psykers harbouring daemons or possessing destructive powers.[1]
The Black Ship Captains are responsible for weeding them out and destroying them before they reach as far as Terra. A few, however, do reach Terra despite these vigorous precautions, and in the past important officials of the Imperium (even High Lords) have been psykers of this sort.[1]
Sources
- 1: White Dwarf 140 (UK), pg. 54