Fallacy means a flaw in a person's argument, a sort of logical failure. However, these are designed to play into the emotions of the listener causing them to believe it anyway.

Fallacy is a false conception that results from faulty reasoning. It is not always intentional, sometimes it's a conclusion that comes from valid research, but the conclusion does not make logical sense. Sometimes though it is made intentionally with the purpose to deceive. Another way of looking at a fallacy is that it may appear to be true on the surface but after continued research, it proves to be false.