Posthuman or post-human is a concept originating in the fields of science fiction, futurology, contemporary art, and philosophy that means a person or entity that exists in a state beyond being human. The concept addresses questions of ethics and justice, language and trans-species communication, social systems, and the intellectual aspirations of interdisciplinarity.
Posthumanism is not to be confused with transhumanism (the nanobiotechnological enhancement of human beings) and narrow definitions of the posthuman as the hoped-for transcendence of materiality. The notion of the posthuman comes up both in posthumanism as well as transhumanism, but it has a special meaning in each tradition. In 2017, Penn State University Press in cooperation with Stefan Lorenz Sorgner and James Hughes established the "Journal of Posthuman Studies", in which all aspects of the concept "posthuman" can be analysed.
In critical theory, the posthuman is a speculative being that represents or seeks to re-conceive the human. It is the object of posthumanist criticism, which critically questions humanism, a branch of humanist philosophy which claims that human nature is a universal state from which the human being emerges; human nature is autonomous, rational, capable of free will, and unified in itself as the apex of existence. Thus, the posthuman position recognizes imperfectability and disunity within oneself, and understands the world through heterogeneous perspectives while seeking to maintain intellectual rigor and dedication to objective observations. Key to this posthuman practice is the ability to fluidly change perspectives and manifest oneself through different identities. The posthuman, for critical theorists of the subject, has an emergent ontology rather than a stable one; in other words, the posthuman is not a singular, defined individual, but rather one who can "become" or embody different identities and understand the world from multiple, heterogeneous perspectives.
Critical discourses surrounding posthumanism are not homogeneous, but in fact present a series of often contradictory ideas, and the term itself is contested, with one of the foremost authors associated with posthumanism, Manuel de Landa, decrying the term as "very silly." Covering the ideas of, for example, Robert Pepperell's The Posthuman Condition, and Hayles's How We Became Posthuman under a single term is distinctly problematic due to these contradictions.
The posthuman is roughly synonymous with the "cyborg" of A Cyborg Manifesto by Donna Haraway. Haraway's conception of the cyborg is an ironic take on traditional conceptions of the cyborg that inverts the traditional trope of the cyborg whose presence questions the salient line between humans and robots. Haraway's cyborg is in many ways the "beta" version of the posthuman, as her cyborg theory prompted the issue to be taken up in critical theory. Following Haraway, Hayles, whose work grounds much of the critical posthuman discourse, asserts that liberal humanism--which separates the mind from the body and thus portrays the body as a "shell" or vehicle for the mind--becomes increasingly complicated in the late 20th and 21st centuries because information technology puts the human body in question. Hayles maintains that we must be conscious of information technology advancements while understanding information as "disembodied," that is, something which cannot fundamentally replace the human body but can only be incorporated into it and human life practices.
The idea of post-posthumanism (post-cyborgism) has recently been introduced. This body of work outlines the after-effects of long-term adaptation to cyborg technologies and their subsequent removal, e.g., what happens after 20 years of constantly wearing computer-mediating eyeglass technologies and subsequently removing them, and of long-term adaptation to virtual worlds followed by return to "reality." and the associated post-cyborg ethics (e.g. the ethics of forced removal of cyborg technologies by authorities, etc.).
Posthuman political and natural rights have been framed on a spectrum with animal rights and human rights. Posthumanism broadens the scope of what it means to be a valued life form and to be treated as such (in contrast to certain life forms being seen as less-than and being taken advantage of or killed off); it "calls for a more inclusive definition of life, and a greater moral-ethical response, and responsibility, to non-human life forms in the age of species blurring and species mixing. ... [I]t interrogates the hierarchic ordering - and subsequently exploitation and even eradication - of life forms." 
According to transhumanist thinkers, a posthuman is a hypothetical future being "whose basic capacities so radically exceed those of present humans as to be no longer unambiguously human by our current standards." Posthumans primarily focus on cybernetics, the posthuman consequent and the relationship to digital technology. The emphasis is on systems. Transhumanism does not focus on either of these. Instead, transhumanism focuses on the modification of the human species via any kind of emerging science, including genetic engineering, digital technology, and bioengineering.
Posthumans could be completely synthetic artificial intelligences, or a symbiosis of human and artificial intelligence, or uploaded consciousnesses, or the result of making many smaller but cumulatively profound technological augmentations to a biological human, i.e. a cyborg. Some examples of the latter are redesigning the human organism using advanced nanotechnology or radical enhancement using some combination of technologies such as genetic engineering, psychopharmacology, life extension therapies, neural interfaces, advanced information management tools, memory enhancing drugs, wearable or implanted computers, and cognitive techniques.
As used in this article, "posthuman" does not necessarily refer to a conjectured future where humans are extinct or otherwise absent from the Earth. As with other species who speciate from one another, both humans and posthumans could continue to exist. However, the apocalyptic scenario appears to be a viewpoint shared among a minority of transhumanists such as Marvin Minsky and Hans Moravec, who could be considered misanthropes, at least in regard to humanity in its current state. Alternatively, others such as Kevin Warwick argue for the likelihood that both humans and posthumans will continue to exist but the latter will predominate in society over the former because of their abilities. Recently, scholars have begun to speculate that posthumanism provides an alternative analysis of apocalyptic cinema and fiction, often casting vampires, werewolves and even zombies as potential evolutions of the human form and being.
Many science fiction authors, such as Greg Egan, H. G. Wells, Isaac Asimov, Bruce Sterling, Frederik Pohl, Greg Bear, Charles Stross, Neal Asher, Ken MacLeod, Peter F. Hamilton and authors of the Orion's Arm Universe, have written works set in posthuman futures.
A variation on the posthuman theme is the notion of a "posthuman god"; the idea that posthumans, being no longer confined to the parameters of human nature, might grow physically and mentally so powerful as to appear possibly god-like by present-day human standards. This notion should not be interpreted as being related to the idea portrayed in some science fiction that a sufficiently advanced species may "ascend" to a higher plane of existence--rather, it merely means that some posthuman beings may become so exceedingly intelligent and technologically sophisticated that their behaviour would not possibly be comprehensible to modern humans, purely by reason of their limited intelligence and imagination.