Déjà vu, a French phrase meaning “already seen,” (中文： 似曾相識）has fascinated researchers and layfolk alike for centuries.
From Wikipedia:
"Déjà vu ("already seen") is the phenomenon of feeling as though one has lived through the present situation before. It is an illusion of memory whereby—despite a strong sense of recollection—the time, place, and context of the "previous" experience are uncertain or impossible"
Note per informal American English, "déjà vu" is slang for something that is very familiar or has happened many times before. For example, you might say "The rise in housing costs is déjà vu all over again".
What makes it more interesting is that déjà vu, by Wiki definition, is a common experience, affecting about two-thirds of people, with young people experience it more often. Also it's difficult to study déjà vu in a laboratory because researchers can't stop someone in the middle of an episode to examine their brain.
- Source: online
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I have heard the phrase multiple times before, but it didn't click for me until a few nights ago: I had a dream of flying in the sky and it ain't the first time. No, I wasn't flying in an airplane, but all by myself without wings!! 
. Each time when the dream starts, I would feel that I flew like this before, especially that desperate feeling of no matter what I try, I just couldn't go fast ... ... So, here is my déjà vu. 
But, if we go by the definition of informal American English as above, all of us have had some of these déjà vu moments (like what will happen tomorrow happened 8 years ago).
Alright, enough of déjà vu, let's go back to real life and cheer for what we have, and have a happy Sunday!
