the phenomenon among thin women of the fronts of their panties not touching their lower abdomens. This phenomenon is best achieved when the woman is lying on her back. The front of the panty is held up and away from her concave lower abdomen by her hip bones and the bulge of her vulva/pubic mound. Panty canopies are considered attractive by many not only because they demonstrate the thinness of the woman but, when viewed from the proper angle, provide a view of the top of the woman's vulva/pubic mound. (See also panty bridge, which is a subset of the panty canopy.)
That model is showing off how thin she is by lying down, sucking in her already tiny abdomen, and creating a panty canopy so deep that a train could drive under it.