expression, godan verb (-su)
have an involuntary emission of semen
Medical or formal term for nocturnal emission or involuntary seminal discharge. Not used in casual conversation.
思春期の男子は、睡眠中に精を漏らすことがある。
Adolescent boys sometimes have involuntary emissions of semen during sleep.
夢精 is the common noun for nocturnal emission or wet dream, while 精を漏らす is a more clinical, descriptive phrase.
Compound of 精 (semen) + を (object marker) + 漏らす (to let leak). The exact historical origin is uncertain, but it is a straightforward descriptive phrase.