definition of endgame

Please show me where the definition of an endgame exists. An IM told me it is when queens are off the board regardless of other pieces still there. I keep reading lots of guesses but nothing concrete to know that 2 players are in an endgame.

There is no definition or diagram that explains when it's endgame time.  There is such a thing as a queen + pawn ending and also a queenless middlegame.

In general it is when the queen is off and some pawns and pieces have been exchanged and a clear plan is thought up (good example is to target a pawn that has been weak since the middle game).  The position is no longer very dynamic but can be tricky.  Also when king activity becomes important.

 You should be able to feel when it's and endgame yourself.  Just remember it is when it is less dynamic or when deep/strategic considerations are not important.

To me is when the king can and should unleash all his hidden power. Power to lose some weight in queen endgames, but power after all.

I agree with Pulpofeira. You can often recognize the end game when the king starts to travel a lot or become a more important piece relative to the remaining pieces. Typically, the position is also simplified to the point where it's much easier to calculate many moves in advance. It doesn't make sense to try to make a strict rule as to which and how many pieces remain on the board.

Note that in the mid-game there are normally still a lot of strong lines where the king can stay put or hide. 

I believe in his book "Practical Endgame Play - Beyond the Basics", Glenn Flear defines a typical endgame as a situation where each player only has one (or fewer) pieces, besides kings and pawns.

This works well for the premise of his book, because the book is specifically focused on teaching players how to handle "Not Quite Endgames" (NQEs), which is situations with two pieces remaining on one or both sides.

Personally, I haven't gotten far enough in my endgame study for it to matter. If I ever get around to finishing Silman's Complete Endgame Course, that will probably be on my list of endgame books to consider studying next. But I'm doing too much chess study of various things, so I'm not just focused on endgames, and it'll take me a long time to get there.

Dvoretsky in his 'Endgame Manual' says he will only deal with position where each play only has a maximum of one piece. Shereshevskii in 'Endgame Strategy' deals with multiple pieces. I worked through the latter a few years ago and it seems more like 'Late Middlegame'  to me. How long is a piece of string ? IMHO, it is as long as Dvoretsky says it is, because I feel this is where the 'work has to be done', and where you have to ' eat your greens'.