Meaning: This describes the way that the moonlight makes the lake look like it is shining with a soft, silver light.
Choice of Words: "Moon" is the natural satellite of Earth, and "cast" means to throw or send out. "Silver" is a color that is like the color of silver metal, and "glow" means to shine with a soft light. When the moon casts a silver glow on the lake, it means that the moonlight makes the lake look like it is shining with a soft, silver light.