surface, typically glass coated with a metal amalgam, which reflects a clear image

A mirror or looking-glass is something that reflects light. One common plane mirror is a piece of special flat glass that a person can look into to see a reflection of themselves or what is behind them.

A framed mirror showing a jug.
A fish pond acting as a mirror to reflect views of people.
Marie Wandscheer: 'Before the Ball' (1886)

Sometimes, a flat piece of metal or the surface of water can act like a mirror.

People can see themselves in a mirror because light comes in and is reflected.

Curved mirrors can have magnification properties, making images appear smaller or larger than their actual size, like a lens does.. They can be concave (curved inward) or convex (curved outward), making the reflected angle and view to be smaller or larger, respectively. Special mirrors can make a person's appearance look quite strange.

Also, in a mirror, writing appears backwards, as a "mirror image" of the original writing.

Mirrors are usually made out of glass with metal on the back, called "silvering" even if the metal is not silver. Modern mirrors use aluminum. The aluminum is applied via vacuum, and will bond directly to cooled glass.