Abhuman is a general term for creatures that are, to some extent, human but altered somehow by numenera. Mutants, crossbreeds, and genetically engineered are all classified as abhumans. Abhumans are distinct from visitant in that abhumans are native to earth. Most abhumans are sentient, some are rational, some peaceful. Others are monsters that kill without reason.
Mutants are humans who have changed over time, either through natural forces of evolution or through an unnatural manipulation to an individual or his ancestors. Unnatural manipulation could mean exposure to mutagens, the result of genetic engineering, or the result of genetic engineering gone wrong.
In the Ninth World, mutants sometimes band together. Those with hideous deformities face discrimination and derision. Some are outcasts, others are revered, flaunting their mutations as a sign of superiority, power, and influence. Their mutations are seen as a blessing, not a curse. Some people believe them to be divine.