The penis is an external reproductive organ. The urethra passes through the length of the penis and allows urine and semen to exit the body. The penis has two distinct parts: The head (glans) and the shaft. In uncircumcised people, foreskin covers the head of the penis.
When sexually aroused, the spongy erectile tissue in the penis becomes engorged with blood. When this happens, the penis becomes erect, or hard. This makes it possible for the penis to be inserted into the vagina or anus during sexual intercourse. The friction during intercourse then stimulates the sensitive nerve endings in the penis, which can eventually lead to ejaculation and orgasm.
The penis has a number of nicknames, including cock, pecker, and dick.