Common synonyms for "crank" include crackpot and kook. A crank differs from a fanatic in that the subject of the fanatic's obsession is either not necessarily widely regarded as wrong or not necessarily a "fringe" belief. Similarly, the word "quack" is reserved for someone who promotes a medical remedy or practice that is widely considered to be ineffective; this term, however, does not imply any deep belief in the idea or product they are attempting to sell. "Crank" may also refer to an ill-tempered person or one who is in a bad mood, but that usage is not the subject of this article.