A mirror is a smooth, reflective surface that shows you an image of whatever is in front of it. Most mirrors are made of glass with a thin coating of metal (usually aluminum or silver) on the back. When light bounces off this metal layer, it creates a reflection that looks just like the real thing, only reversed left to right.

You see mirrors everywhere: bathrooms, car side-view mirrors, dressing rooms, even inside telescopes and lasers. Ancient people made mirrors from polished bronze or obsidian (volcanic glass), but they weren't nearly as clear as modern glass mirrors.

The word also means to reflect or copy something closely. A calm lake can mirror the sky above it, creating a perfect upside-down image of clouds and mountains. When someone mirrors your behavior, they're copying your gestures or expressions, often without realizing it. Friends who spend lots of time together sometimes start mirroring each other's speech patterns and body language.

Scientists use special mirrors in powerful telescopes to gather light from distant stars. The James Webb Space Telescope has mirrors coated in gold because gold reflects infrared light better than silver does. These mirrors had to be polished so precisely that if they were scaled up to the size of the United States, the biggest bump would be only two inches tall.