While chatting with a new colleague for the first time, a 31-year-old man is suddenly gripped by an intense, specific certainty that this exact conversation has happened before, word for word. The feeling lasts only a few seconds before fading, leaving him slightly unsettled but otherwise unbothered, and he knows perfectly well it cannot actually have happened before. What is this?

This is déjà vu: a vivid, specific feeling that a current situation has already been experienced, despite there being no factual basis for it, and with the person's own recognition that it cannot really have happened. It is not cryptamnesia, which involves genuinely previously encountered material being reproduced and mistaken for an original creation, rather than a new experience feeling falsely familiar. It is not a genuine forgotten memory, because there is no actual prior encounter here. And it is not a delusion, because the conviction is brief and the man retains full insight that it is 'just a feeling,' not a fixed false belief.