A mirror is a glass surface backed with a metallic coating that reflects images that are in front of it. When you gaze at yourself in a mirror, your own face gazes right back at you.
"Mirror, mirror on the wall, who's the fairest of them all?" asks the evil queen in "Snow White," as she admires her reflection. Ordinary mirrors can't answer this question, but they can show you how you look in your new hat or whether you have spinach between your teeth. And the verb mirror means "reflect," as when the surface of a lake mirrors the sky.