The meaning of the phrase "Wet Behind the Ears" is someone who is very young, naive and inexperienced.
Example of use: "I can't believe they decided to promote Kelly. If you ask me, I think she's still wet behind the ears".
The origin of the phrase "Wet behind the ears" is debatable. Some say it comes from newborn babies who enter the world surrounded by amniotic fluid. Others say the phrase may have originated from newborn farm animals, where the mother has to lick the newborn dry, and one of the last places she dries is the area behind the ears. However the difference between the two, is the fact that when human babies are born, they are helpless, vulnerable and premature, relative to other species.