Hermaphroditus, the two-sexed child of Aphrodite and Hermes, “intersex” generic name (when there is a lack of concordance between the genetic sex and the anatomical one).
Intersex, in humans and other animals, is a variation in sex characteristics including chromosomes, gonads, and/or genitals that do not allow an individual to be distinctly identified as a male or female. Such variation may involve genital ambiguity and combinations of chromosomal genotype and sexual phenotype other than XY male and XX female. Intersex infants with ambiguous outer genitalia may be surgically corrected to more easily fit into a socially accepted sex category. Others may opt, in adulthood, for surgical procedures and/or hormonal treatments in order to align their physical sex characteristics with their gender identity  or the sex category to which they were assigned at birth. Others will never become aware that they are intersex _ unless they receive genetic testing _ because it does not manifest in their phenotype. Some individual may be raised as a certain sex (male or female) but then identify with another later in life while others may not identify themselves as either exclusively female or exclusively male.
Intersexuality as a term was adopted by medicine during the 20th century. Intersex conditions received attention from intersex activists, who criticized traditional medical approaches in sex assignment and sought to be heard in the construction of new approaches. The passports and identification documents of some nationalities (Australian first in 2011) have adopted “X” as a valid third category besides “M” (male) and “F” (female).
Research in the late 20th century has led to a growing medical consensus that diverse intersex bodies are normal forms of human biology 1/2000 births in the world (that’s an impressive number). Contrary to Western common belief, there are no just two sexes, although the term third gender and third sex describes individuals who are categorized by their will or by social consensus as neither man or woman, while on top of the male and female categories there are three major sub-groups at least!  Nevertheless France, the Swiss Ethical committee and United Kingdom have just rejected the possibility of the third category “X” besides “M” and “F” on identification documents. In France it is even worse, we still assign a sex category at birth, while in Swiss they wait until the biological maturity of the child to let him/her choose a sex category.
 See the work of Pr John Money, a psychologist sexologist and author specializing in research into sexual identity and biology of gender; the term “gender” was coined first time by him as the “psychological sex”.
 See the seminal work of Pr Anne Fausto-Sterling “The five sexes…” http://capone.mtsu.edu/phollowa/5sexes.html