Abhumans are human subspecies - descendants of humans who have physically evolved after long periods of isolation on worlds with various extreme environmental conditions.
In an Imperium where genetic mutation and spiritual corruption are often interrelated, abhumans are a focus of much controversy. In more liberal times under the Emperor, even markedly divergent abhumans such as the Beastmen could serve in the Imperial Guard. Since the Emperor's stasis however, only the lesser deviants, such as Ogryns and Ratlings, are considered Imperial citizens. However, they are still distrusted by the more puritan members of the Inquisition.