The transmission of mental symptoms has been given different names: induced delusional disorder, shared psychosis, folie à deux, trois, quatre, or millions—depending on the number affected.

All describe the same phenomenon. Shared psychosis captures the syndrome-like severity, but is a misnomer because it often does not involve actual psychosis.  Folie à deux, or "madness in two," is perhaps the most preferred. The important feature is that mental symptoms are not confined to the person; they take hold and spread across interpersonal boundaries.

Severe psychopathology in an influential figure transmits to others or a group, until the exposed persons or groups come to feel, think, and behave as if they had the same disorder as the primary person. Exposure to actual delusions is unlike exposure to strategic lies or simple misinformation; they are more infectious because the primary person is genuinely convinced of them.

THE PASSAGE ABOVE IS FROM A 2020 ARTICLE LOCATED HERE.