The following glossary is adapted from the glossary provided by Planned Parenthood at https://www.plannedparenthood.org/learn/glossary.
Rectum: The lowest end of the intestine before the anus, where solid waste (feces) is stored.
Refractory period: The time after ejaculation during which a man is not able to have an erection.
Reproductive cell: A unique cell — egg in women, sperm in men — that can join with its opposite to make reproduction possible.
Reproductive organs: In women: the fallopian tubes, ovaries, uterus, and vagina. In men: the penis, prostate, and testes.
Rhythm method: Outdated name for what is now called the calendar method of fertility awareness.
Rugae: The folds of tissue in the walls of the vagina.