Coined by the new Jersey Shore girl, Deena Nicole.
A female backpack is a female who gets into a relationship and looses sight of everything else other than the guy she is dating. She spends all of her time focused on her significant other, does whatever he does, and goes wherever he goes.
Simply put wherever her boyfriend goes she goes, because she is on his back 24/7.
“She’s probably sitting there watching Ronnie lift … She’s Ronnie’s backpack. She’s a female backpack.”