look up any word, like fellated:
When one's parents forget it is your birthday because you are the fourth child. They have celebrated the other three kids birthdays, and told you about it, but forget yours.
I am thinking of calling my parents tonight to remind them it is my birthday---but then they will feel bad they have forgotten it. That is the essence of "FCS or Fourth Child Syndrome".
by Auntie N September 18, 2010