A talking mirror is a mirror which advises anybody who looks into it on how to improve their appearance. Both the Weasley family and the Leaky Cauldron own one. Talking mirrors also seem to have a personality, as the one in the Weasleys' seemed to be brusque and rude, ordering people rather than advising, where as the one in the Leaky Cauldron, which, when Harry Potter tried flattening his hair, said "You're fighting a losing battle there, dear."