The glossy sheen of cling film stretched over something, catching the light in narrow bright streaks that follow the shapes underneath.
Like relief() and chrome() it treats brightness as height and lights the result, but its highlights are narrow and bright rather than broad, which is the difference between plastic and stone.
detail runs the opposite way to what you might expect. Higher settings mean a *smaller* blur before the height is read, which leaves finer contours in the surface and therefore more numerous, thinner streaks of sheen. Lower settings smooth the surface out and give a few broad highlights instead.
The result is composited over the original picture, so the colours show through the film rather than being replaced by it.