Déja vu, pronounced Déjà vi, is a French term meaning “seen”. Déjà vu is a psychological reaction that makes the brain transmit to the individual that he has been to that place, without ever having been there, or that he knows someone, but that he has never seen it before.
Déjà vu is a sensation that occasionally arises, it occurs when we do, say or see something that feels like we've already done or seen it before, but it never happens. Déjà vu appears as a “replay” of some scene, where the person is sure that they have already gone through that moment, but it never really happened.
Déjà vu occurs because the brain has several types of memory, such as immediate memory, which is capable of repeating a phone number and then forgetting them. Short-term memory lasts a few hours and long-term memory lasts months or even years. Déjà vu is actually a flaw in the brain, where the facts that are happening are stored directly in the memory of long or medium term, when the correct thing would be to go to immediate memory, thus giving the feeling that the event has already occurred before.