Endgame principles in chess refer to strategies and tactics that players use when there are fewer pieces left on the board. Key concepts include the importance of king activity, pawn promotion, and controlling key squares. Players aim to simplify the position by exchanging pieces when they have a material advantage, making it easier to convert that advantage into a win. Another essential principle is the concept of opposition, where one player positions their king directly opposite the opponent's king to control the game. Understanding these principles helps players make informed decisions and increases their chances of success in the endgame phase of a match.