The Go board can be thought of as having nine regions, if you imagine breaking it into squares of the same size, like a tic tac toe board. Later in the game you may have developed such a strong position in the "northwest" region of the board that when your opponent places a stone there, it isn't important for you to respond immediately in that region - it'd take many turns for your opponent to have a chance of being a real threat in that area. So, you play elsewhere on the board.