A table screen is a slab of stone set in a stand so it can stand upright — originally a way to display a piece of fine material, later a format for carving in its own right. The nephrite here is cut thin so light passes through it, which is how the carver shows off the stone.
Nephrite is properly one of only two minerals called jade, and it is identified clearly here rather than left as a vague "jade" claim. The slab is held in a carved frame; lift the screen by the frame, never by the stone, and keep it out of direct sun.