Like the missionary position, but with the penetrating partner reaching under the receiving partner's behind and gripping both of their hips firmly, while simultaneously extending their self forward such that the penetration angle is nearly 90 degrees. Because the penetrator is holding the receiver's hips, the penetrator is able to achieve maximum control over thrusting.
This position is supposedly common among young people on college campuses, because it requires a great deal of physical exertion (at least by the penetrating partner).