A female, typically under the age of 30 who loves to publicly exhibit her armpits when excited in some way by pumping her fists into the air while shouting WOO! (sometimes WOO WOO). Whilst alcohol is a typical prequisite to becoming a WOO girl, it is not required.
A gathering of Woo-girls say, "Hey, look at that hot guy ..... WOO!" while pumping their fists high overhead