Occlumency

Occlumency is, in the fictional realm of J.K. Rowling's Harry Potter series, a branch of magic involving the practice of closing one's mind against outside penetration, thereby preventing others from reading one's thoughts. This nonexistent word was created by joining the word "occlude" (which means to close or block off) with the suffix "-mancy" (which means divination).

In Harry Potter and the Order of the Phoenix, former Death Eater Severus Snape teaches student Harry Potter to stop mental attacks from the evil Lord Voldemort.