Transhumanism is a subculture/movement rallied under the idea "If the future can’t be now, it should be as soon as possible." Hence, it encourages research into life extension, cryonics, nanotech, physical/mental enhancements, megascale engineering and AI. T.S. Eliot wrote of the "process by which the human is Transhumanised", as the human journey towards illumination, in his comedy of manners The Cocktail Party. British biologist Julian Huxley in New Bottles For New Wine, had an essay "Transhunism" in which he argued how humans must establish better environments for themselves, and allueded to the new species that humans might eventually become. In 1990, Dr. Max More first published "transhumanism" as a philosophy, differing from Huxley in that he believed in "man remaining man but transcending himself."
Soon after, transhumanism took off as a social movement (casting off its capital T and quotation marks). There are two major types of transhumans:

Extropian, a transhuman who wants to live forevever, by means of cloning, cryonics, or genetic altering. Tries to augment his consciousness through technology and drugs, consequently often espousing libertarian political views.

Singularitarian, a transhuman who seeks immortality by merging with computers to become an immortal new life-form. This hypothesized future is the "singular" event in human history.

Conceptually, as well as etymologically, the transhuman is very similar to the superman of German philosopher Fiedrich Nietzsche. Nietzsche’s self-overcoming is rephrased, but with little change in meaning, in More’s ideas on man’s self-transcendance. The cutting-edge interdisciplinary interest in life-enhancing technology is in line with Nietzsche’s emphasis on life-enriching philosophy. Meanwhile, the underlying transhumanist search for immortality seems to be a manifestation of Nietzsche’s will to power.

Know Your Transhumanists, Wired.