The foreskin or prepuce (a technically broader term that also includes the clitoral hood, the homologous structure in women) is a retractable double-layered fold of skin and mucous membrane that covers the glans penis and protects the urinary meatus when the penis isn't erect. Contrary to popular belief, it doesn't always automatically retract during an erection. Almost all mammals have foreskins, although in these non-human cases the foreskin is usually a sheath into which the whole penis is r… (More on Foreskin)