Dark Arts is a colloquial term for techniques or methods which involve deception and/or manipulation of others or oneself. Some use the term to refer more narrowly to techniques that work equally well to compel both true and false beliefs, i.e., they are symmetric weapons.
An example from the Dark Arts of Rationality:
Today, we're going to talk about Dark rationalist techniques: productivity tools which seem incoherent, mad, and downright irrational. These techniques include: