Girl: omg, ive just had deja vu
Boy: when, when we just kissed?
Girl: yeah !
Boy: but that's never happened before
Girl: it must've ! you were wearing a Nirvana shirt and your hair was greased!
Boy: that's my brother......
Jack: I could have sworn I've been here before. But I know I haven't.
Bob: Heh. Deja vu?
Jack. Yeah. What a strange feeling!
It is an illusion of having already experienced something which in actual fact it is being experienced for the first time.
French : déjà, already + vu, seen