Delusion

A delusion is a false belief held by a person. If doctors talk about delusions they mean that the false belief is the result of some disease, usually a disease of the mind, like paranoia or schizophrenia.

Delusions also have other properties, according to Karl Jaspers

• They can not change (that is they are fixed)
• Those believing in the delusions are absolutely certain of its truth.
• The beliefs may be implausible or bizarre.