Erection is an excited state of a penis. It is like an exclamation point with two points, .! , The erection, or penile erection, is a physiological phenomenon where the penis becomes firmer, engorged and enlarged. Erections are often followed by ejaculations.
Erections during sleep or when waking up are known as nocturnal penile tumescence (NPT). A penis which is partly, but not fully, erect is sometimes known as a semi-erection; a penis which is not erect is typically referred to as being flaccid, or soft. A penile erection is an indicator of sexual arousal and is required for a male to effect vaginal penetration and sexual intercourse. The scrotum may, but not always, become tightened during an erection. Generally, the foreskin automatically and gradually retracts, exposing the glans, though some males may have to manually retract their foreskin. After a male has ejaculated during a sex or masturbation, the erection usually ends, but this may take time depending on the length and thickness of the penis.