The Mirror of Galadriel is a silver basin that was used by Galadriel to see the future, the possible future, or to see the happenings in the distant lands. When left to its own devices, it could show anything.

Galadriel used it to show Frodo what would happen if he had failed at his Quest. She was able to use the Mirror because she bore one of the Rings of Power, Nenya.
Encyclopedia entry originally written by Abraon