Typically used with the preceeding pronoun "her", a metaphor used when having sex/nailing/fucking a girl (commonly referred to as a slut, hoe or bitch) so vigorously that you could visualize splitting her in half up the centre (or up the back, respectively). Usually referring to a slim tall girl, or a cute, tiny petite one.
Often used in the degrading sense by a male among his peers to raise his esteem.
"I picked up the hottest slut at the bar last weekend: she was blonde, fit body, tight ass; the works. We're going out for drinks tonight :D.... I cant wait to take that bitch home and break her in half!"