The term 'abhuman' can refer to many things. While a precise definition is lacking, 'abhuman' generally refers to a person who is not considered fully human by either society or themselves.
The first and most accepted kind of abhuman is a human being who has become an abhuman through technological means. These transhumans, as they are called, augment their bodies with computers and cyberware which, after significant changes, leaves behind a creature made mostly of metal and circuitry rather than flesh and blood.
The next kind of abhuman is a mutant. These abhumans have genetic alterations developed through adaptations to a specific environment, radiation, or genetic modification. If capable of reproducing on their own, these mutants are sometimes regarded as their own species.
The final kind of abhuman is the least tolerated by mankind and is often discriminated against or exterminated; is known as ahumans or antihumans. These abhumans are tainted either by the Aether or by Xenos species.