idiom · literally hiding the sky and covering the sun, often used to describe dense forests, thick clouds, or massive swarms of something.

森林里的原始树木枝繁叶茂，遮天蔽日。

idiom · figuratively describing something of immense magnitude, power, or universal importance that dominates its surroundings.

他的权势在当地遮天蔽日，没有人敢轻易得罪他。