What is the Mirror of Erised?

The Mirror of Erised is a mystical mirror discovered by Harry in a back corridor of Hogwarts School of Witchcraft and Wizardry in Harry Potter and the Philosopher's Stone. On it is inscribed, erised stra ehru oyt ube cafru oyt on wohsi — which, when reversed and correctly spaced, reads I show not your face but your heart's desire. Erised is "desire" spelled backwards. According to Dumbledore, the Mirror "shows us nothing more or less than the deepest, most desperate desire of our hearts".

Quotes from Wikipedia