Occlumency

From Hpwiki

Occlumency is an obscure branch of magic used to ward off attacks on the mind by witches or wizards. Occlumency may be considered to be the opposite of Legilimency, which is used to delve into the thoughts of others.

Witches or wizards who are skilled in Occlumency are called Occlumens.

Albus Dumbledore, Severus Snape and Lord Voldemort are all accomplished Occlumens. It was revealed in Book 6 that Bellatrix Lestrange and Draco Malfoy know Occlumency too, and in Book 5 Severus Snape attempted to teach Harry Potter how to perform Occlumency, but with little success.