It's a frame that eliminates the top tube in favor of lateral tubes running from the head set to the rear dropouts. It provides the benefits of a "ladies" step through frame (i.e., a frame with a sloping top-tube that ends at the seat tube) with frame stability somewhere between the weaker ("ladies") step-through frame and the stronger ("men's") diamond frame. It was designed to be a "unisex" frame (read: "Girl's frame" ).