Intersex, in humans and other animals, is the presence of intermediate or atypical combinations of physical features that usually distinguish female from male. This is usually understood to be congenital, involving chromosomal, morphologic, genital and/or gonadal anomalies, such as diversion from typical XX-female or XY-male presentations, e.g., sex reversal (XY-female, XX-male), genital ambiguity, or sex developmental differences. An intersex individual may have biological characteristics of both the male and the female sexes.Intersexuality as a term was adopted by medicine during the 20th century, and applied to human beings whose biological sex cannot be classified as clearly male or female.Intersex was initially adopted by intersex activists who criticize traditional medical approaches to sex assignment and seek to be heard in the construction of new approaches.

Some people (whether physically intersex or not) do not identify themselves as either exclusively female or exclusively male. Androgyny is sometimes used to refer to those without gender-specific physical sexual characteristics or sexual orientation or gender identity, or some combination of these; such people can be physically and psychologically anywhere between the two sexes. This state may or may not include a mixture or absence of sexual orientation.