Identical to rug-rats, except these are children you only see on a womans internet profile in pics. Be it facebook, myspace, etc.
You know the lady has kids, you just never see them in public. Hence: Webrats.
Guy One: Duuude I met this kick ass chica at the bar last night!
Guy Two: Sweeet man, what's her name?
Guy One: Sarah, why?
Guy Two: Shit kid, that girl is one of my facebook friends. She has webrats!
Guy One: Nooooooooooo!!!