A conspiracy theory is an explanatory proposition that accuses two or more persons, a group, or an organization of having caused or covered up, through secret planning and deliberate action, an illegal or harmful event or situation. In recent decades the term has acquired a derogatory meaning to some, and distinction should be made between the derisive use of the term and reference to actual, proven conspiracies.
Different types of conspiracy theories have been distinguished, ranging from those merely based on a hunch to ones backed by evidence, and from localized, single-event conspiracies to pervading universal phenomena.
While theories on small and large-scale conspiracies are often correct, some psychologists believe that false application of conspiracy theory can be endemic to certain mental illnesses and disorders. Some recent political regimes have misused conspiracy theories to manipulate their subjects.