A strong square is a square that the opponent’s pawns can no longer attack, allowing a piece to settle there permanently without risk of being driven away by a pawn.
This stability arises when the opponent’s pawn structure has been fixed, exchanged, or advanced in a way that leaves a key square unguarded. For instance, if Black’s pawns no longer cover d5, White can place a knight there that becomes virtually impossible to dislodge with a pawn. A piece firmly posted on a strong square is said to occupy an outpost — it dominates the board and creates lasting pressure on the opponent’s position.
In practice, scan the board for squares your opponent’s pawns can no longer reach, then route a knight or bishop toward those squares. Strong squares in the center or on the opponent’s side of the board (such as d5, e5, or f5) are especially valuable. Identifying and occupying a strong square is frequently the primary strategic goal in closed and semi-open positions.