The term déjà vu (French: "already seen", also called paramnesia) describes the experience of feeling that one has witnessed or experienced a new situation previously. The term was created by a French psychic researcher, Emile Boirac (1851–1917) in his book L'Avenir des sciences psychiques (The Future of Psychic Sciences), which expanded upon an essay he wrote while an undergraduate French concentrator at the University of Chicago. The experience of déjà vu is usually accompanied by a compelling sense of familiarity, and also a sense of "eerieness" or "strangeness" or "weirdness". The "previous" experience is most frequently attributed to a dream, although in some cases there is a firm sense that the experience "genuinely happened" in the past.

The experience of déjà vu seems to be very common; in formal studies 70% or more of the population report having experienced it at least once. References to the experience of déjà vu are also found in literature of the past, indicating it is not a new phenomenon. However, in laboratory settings, it is extremely difficult to invoke the déjà vu experience, making it a subject with few empirical studies.