What is a foreskin?

In male human anatomy, Prepuce, more commonly referred to as the foreskin is a retractable double-layered folded tube of skin and mucous membrane that covers the glans (head) of the penis and protects it when the penis is not erect. It is also endowed with a large number of touch sensitive nerves that make it important in delivering pleasure during sexual intercourse or masturbation. The mucous membrane that lines the inside helps in stimulating and lubricating the glans penis and also makes the experience easier and more pleasant for the female pardner.
The foreskin ( also refered to as the prepuce) is the part of the skin of the penis that covers the head of the penis.

In teenagers and adults, the foreskin can slide back to expose the penis head. This frequently occurs during an erection. In infants and children the foreskin does not retract until sometime in childhood, usually by age 12.