When do we reach the endgame? When does the middle-game become endgame? The answer to this question is not cast in stone – but usually a position can be viewed as an endgame position when it is safe for the king to join the other active pieces.
The primary reason why you should train your endgame skill is to help you avoid misplaying the endgame and undo all the hard work you did in the middle-game.
Endgame skill refers to your understanding of the main endgame objectives, your knowledge of typical endgame ideas and important theoretical positions.
Chess Endgame Trainer
Study the essential theoretical endgame positions and improve your understanding of endgame objectives. A good grasp of the “principle of two weaknesses” is an essential aspect of your endgame skill.