Defensive Magical Theory

Defensive Magical Theory is a Hogwarts textbook written by Wilbert Slinkhard. Released in 1995, it was used by Dolores Umbridge in Defense Against the Dark Arts classes to ensure the students were taught defensive magic in a "secure, risk-free way."

One of the book's chapters discusses counterjinxes, which Slinkhard claims are improperly named; the names created are simply to make the jinxes sound more acceptable.