A nocturnal emission or "wet dream" is when a person (man or woman) has an orgasm while sleeping. Wet dreams can begin after a person goes through puberty. Many young people 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 in males 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.
It is harder for women to tell, because vaginal lubrication is not always associated with orgasm.
Wet dreams are natural and harmless. They do not mean that anything is wrong with you. Many people stop having wet dreams if they masturbate often, or once they begin having sexual intercourse on a regular basis.