A nocturnal emission or "wet dream" is when a boy or man has an orgasm while sleeping. Wet dreams can begin after a boy goes through puberty. Many young men have their first orgasm this way. They might not understand what has happened to them, if they have not been taught anything about sex.
Nocturnal emissions are called wet dreams because of the dampness caused by ejaculation and because the orgasm and ejaculation often happen during a sexually exciting dream. Scientists are not sure what causes them. Most sexual dreams do not cause orgasms.
Wet dreams are natural and harmless. They do not mean that anything is wrong with you. Many men stop having wet dreams if they masturbate often or once they begin having sexual intercourse on a regular basis.