A sex organ, or primary sexual characteristic, as narrowly defined, is any of the anatomical parts of the body which are involved in sexual reproduction and constitute the reproductive system in a complex organism; in mammals, these include:
The Latin term genitalia, sometimes anglicized as genitals and genital area, is used to describe the externally visible sex organs, known as primary genitalia or external genitalia: in males the penis, in females the clitoris and vulva.
The other, hidden sex organs are referred to as the secondary genitalia or internal genitalia. The most important of these are the gonads, a pair of sex organs, specifically the testes in the male or the ovaries in the female. Gonads are the true sex organs, generating reproductive gametes containing inheritable DNA. They also produce most of the primary hormones that affect sexual development, and regulate other sexual organs and sexually differentiated behaviors.
A more ambiguously defined term is erogenous zone, subjectively, any portion of the body that when stimulated produces erotic sensation, but always prominently including the genitalia.