According to the Intersex Society of North America, "intersex" is a term used to describe several genetic conditions in which a person's reproductive anatomy doesn't fit the typical male or female molds. It is a socially constructed category used to describe a spectrum of different reproductive types, from overly large clitorises, to undescended male genitalia, to very small penises or highly divided scrotums. Intersex is not a common condition, but hospitals estimate that about 1 in 2000 births results in some abnormal form of genitalia. Cal's 5-alpha-reducatse deficiency syndrome is just one circumstance that results in intersex genitalia, via a gene that must be passed down by both the mother and the father.
In the 1950s, psychologist John Money and his team of medical specialists decided on criteria for determining the gender of intersex infants. The criteria was implemented harmfully and dishonestly by many medical professionals, who would often lie to the families of the intersex children about the nature of the condition. Many young patients received surgery and hormonal therapy without their consent. The procedures often followed very sexist guidelines, sacrificing sexual sensation in "girls" for the preservation of fertility and effectively turning "boys" who didn't have large enough penises into girls.
Much like Eugenides' Dr. Luce, Dr. Money advocated a theory of Gender Neutrality, the idea that gender is learned and not innate. Money tested this theory on a set of identical twin brothers, Brian and David Reimer, one of whom had lost his penis during a circumcision accident. Because of this, Dr. Money decided to raise David as a girl. Despite hormone injections, surgery, and being raised as a "girl" (complete with forced female-style sexual play and frilly dresses), David never truly identified as female, and his parents eventually decided to tell him the truth about his gender. Dr. Money used his case as a success story of his gender theory, but David's life was marked by tragedy, and he and his brother both committed suicide.
Intersex individuals reject the word "hermaphrodite," which means both fully male and fully female. It draws its roots from a Greek myth in which the beautiful young son of Hermes and Aphrodite was joined with the body of a seductive water nymph. The term is politically incorrect, and Eugenides originally received criticism from the intersex community for his use of it in the book. They eventually reached a compromise, in which Eugenides agreed not to refer to any living beings as hermaphrodites, only using it in its historical and legendary manner.