Neither player can checkmate the opponent’s king with any series of legal moves.
Under FIDE Laws, Art 1.3 & 5.2.2, the game ends in a ‘dead position’ when a position has arisen in which neither player can checkmate the opponent’s king with any series of legal moves.
Examples of dead positions involve King vs King, King and Bishop vs King, King and Knight vs King. Note that King and two knights vs King is not a dead position, since there is a series of legal moves which is possible for Black to be checkmated.
