"The mind is not a book, to be opened at will and examined at leisure. Thoughts are not etched on the inside of skulls, to be perused by any invader. The mind is a complex and many-layered thing... It is true, however, that those who have mastered Legilimency are able, under certain conditions, to delve into the minds of their victims and to interpret their findings correctly."
-- Severus Snape (OP24)
Legilimency is the ability to extract emotions and memories from another person’s mind. It is a branch of magic not normally taught at Hogwarts (at least, not at Ordinary Wizarding Level). Although the word literally translates as ‘mind-reading’, this is considered a naive interpretation of the art by its practitioners. Someone who practices Legilimency is known as a Legilimens.
legens - (Latin) a reader mens - (Latin) mind