calendar method; fertility awareness method; rhythm method: Natural family planning method of birth control that relies on abstinence during the time of month when the woman is fertile and likely to become pregnant.

candidiasis; yeast infection: Fungal infection that is sometimes spread to the genitals through sexual contact (usually oral sex).

cervical cap: Barrier method of birth control using a small cap that fits tightly over the cervix, blocking sperm from entrance.

cervical mucus method: Natural family planning method of birth control that uses the consistency of the woman’s cervical mucus to determine when a woman is ovulating and therefore fertile.

cervix: The entrance to the uterus in a female’s anatomy.

chlamydia: Most common sexually transmitted disease in the United States; hard to diagnose but treatable.

circumcision: The surgical removal of the penis foreskin.

climacteric: Period of change when a woman goes through menopause, usually lasting one to two years.

clitoris: Part of the female genitalia, found within the vulva and the principal organ of female sexual pleasure.

condom: Barrier method of birth control using a sheath that fits over the penis; the best method of protection against sexually transmitted diseases.

contraception; birth control: The effort to avoid unintended pregnancy via a variety of methods; does not necessarily protect against sexually transmitted disease.

corpus cavernosa: Two spongelike cylindrical tubes that contain the central arteries and lie on the top half of the penis.

corpus spongiosum: A spongelike structure under the two corpus cavernosa that surrounds the urethra and is the pipeline for both urine and sperm.

crus: The penis that is under the skin and not exposed; the proportion of crus to exposed penis is what results in curvature in an erect penis.

cunnilingus: Oral-vaginal sex.