Ko is a situation involving capture and immediate recapture Ko is illegal without another move first, elsewhere on the board, since a board position can't be repeated twice In the example to the right you see white has just taken blacks stone Black can not return the take and thus must move elsewhere
A board position which requires a player to make a move elsewhere before recapturing after the opponent has just captured a stone, to avoid recreating a former board position One of the key strategic elements of the game