wet dream 
noun
An erotic dream that causes involuntary ejaculation of semen.As far as I can tell/recall, part of this is popular superstition - quack medicines exist to prevent the loss of semen through wet dreams as this is attributed to a loss of health and vitality....
- Boys sometimes have wet dreams, which means they ejaculate in their sleep.
- When you think about it, crushing on a goofy cartoon kid was ten times less embarrassing than having wet dreams about this guy.