Dianetics is an alternative mental health therapy created by science fiction writer L. Ron Hubbard, who published a book on the subject in 1950 under the name "Dianetics: The Modern Science of Mental Health". It is about the way people think. Hubbard also started the religion of Scientology, which uses Dianetics.
The photo at the right shows a person learning about Dianetics by doing a stress test. The idea of the stress test is to show people something in their own minds.
Most psychologists think that Dianetics is a pseudoscience. That means that it is not really a science, and it only looks like one.