Oocyte

The female gamete known as an egg or ovum. 

Oral contraceptive

Pills that contain synthetic estrogen and/or progesterone which cause a "false pregnancy" thereby preventing ovulation therefore preventing pregnancy. A popular form of contraceptive and extremely effective when taken properly. 

Oral sex

Sexual activity in which the mouth and tongue are used to sexually stimulate the genitals. 

Orgasm

An intense physical sensation that occurs at the peak (climax) of sexual excitement that is accompanied by rhythmic muscle contractions and intense pleasure. In men the inner pelvic muscles contract causing ejaculation of semen. In women the walls of the vagina and uterus contract also causing ejaculation in some women followed by the release of sexual tensions.

Orgasmic disorder

A difficulty or inability to achieve orgasm.  May be psychological or physical in nature.

Orgasmic platform

The increased blood flow that occurs in the outer third of the vagina during sexual arousal.

Orgy

A gathering of people in engaging in group sex.

Os

The opening of the cervix in which sperm passed through and blood passes out.

Outer lips

The cushiony pads of tissue on both sides of the vaginal opening and inner lips. Also known as the labia majora.

 Ovaries

The two reproductive organs located on both sides of the uterus  responsible for producing ova, estrogen and progesterone.

Ovulation

The maturation and release of an egg from the ovary.

Ova

Plural for ovum also called eggs, oocytes or female gametes.

Ovulate

To release a matured egg from the ovary.

Ovum

Singular for ova.

Oxytocin