What is a Deja vou?

The term "déjà vu" describes the experience of feeling that one has witnessed or experienced a new situation previously.

The experience of déjà vu is usually accompanied by a compelling sense of familiarity, and also a sense of "eerieness", "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. Déjà vu has been described as "Remembering the future".

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.

You have a very detailed article in the http://en.wikipedia.org/wiki/Deja_Vu

Deja vu literally means already seen. It is a phenomenon in which a person encounters a place or situation where they have never been before, but it seems familiar to them as if they have been there before.

There is a hypothesis that deja vu occurs due to a glitch in the brain's processing of visual information. Each eye has a separate optic nerve connected to the brain, and the input from  each eye is received separately and processed in the brain to create a single three-dimensional picture. If a problem occurs in the reception or processing of the information from one eye then the information is somehow received separately and the brain treats it as a separate input. This creates a feeling of already having seen this place (or whatever).

If you will ask Trinity... "A deja vu is usually a glitch in the

LOL!!!