Intersex people

According to the UN Office of the High Commissioner for Human Rights:

Intersex people are born with sex characteristics (including genitals, gonads and chromosome patterns) that do not fit typical binary notions of male or female bodies. Intersex is an umbrella term used to describe a wide range of natural bodily variations. In some cases, intersex traits are visible at birth while in others, they are not apparent until puberty. Some chromosomal intersex variations may not be physically apparent at all.

Every year in the USA, approximately 1 in every 2,000 babies are born with an intersex variation.