Deja Vu Question

I have got a burning question that needs answering!

So my friend and I had a little disagreement over what "experiencing deja vu" actually is. We both had different ideas and they're both pretty valid so now I am just confused and that is not a happy place to be.

Is the correct version of deja vu:
1) It's when you've actually had a similar situation happen to you twice and it feels like it's the first one happening all over again during the second time.
2) It's just your brain playing tricks on you where you think the situation you're in at that moment has already happened down to the smallest of the small details and you are utterly convinced that everything happen the exact same way but in reality it's just you making it up.
3) Something entirely different that you will helpfully enlighten me on in the comments.

Anything you guys say would be very much appreciated!

UNRELATED COMMENT QUESTION: What is your favourite episode of Arthur? I'll tell you mine, you only need to ask :)