Intersexed

Sex anatomy is thought of as occuring in two ways - male or female.  This way of separating sex is inaccurate in that even genetic testing cannot guarantee that you will know what sex characteristics a person will have.  Because we have only two categories of sex, most people are assigned a category at birth and are expected to stick to that category throughout their lives.

Depending on what hormones affect a fetus during its developement, fetal gonads differentiate into various configuations.  Intersexed people's developement didn't settle to one of the extremes of genital differentiation.