Weak Squares

Most club players use "weak square" to mean any square an enemy piece has landed on without being immediately kicked out. That's too loose to be useful. A square is only weak in the strategic sense that matters if no pawn of the defending color can ever attack it again — because a pawn move, unlike almost anything else in chess, cannot be undone. A square an enemy knight currently occupies but that your own pawn could challenge in two moves isn't weak, it's just temporarily occupied. Getting this distinction right is what separates a real long-term plan from chasing a piece around the board.

Where the permanent holes actually come from

Weak squares are created almost entirely by pawn moves, which makes them self-inflicted in a way most weaknesses aren't. Pushing a pawn from e6 to e5 gains space but permanently removes that pawn's ability to ever again cover d6 or f6 — those squares are now holes for as long as the position lasts. A fianchetto structure that later loses its fianchetto bishop leaves every square of that bishop's color permanently uncontested by a piece that used to guard them, which is a related but distinct problem covered on its own page. The common thread is that the weakness is created the moment the pawn moves, whether or not an enemy piece is anywhere nearby to exploit it yet.

A weak square is only worth what reaches it

Identifying a hole in the opponent's structure is the easy half of the skill; the harder half is checking whether you actually have a piece that can get there and stay there usefully. A knight is normally the best tenant, because it can't be challenged by a bishop of the wrong color and doesn't care that the square is a single color. A bishop can also settle on a weak square of its own color, though it's easier to trade off than a knight once it arrives. If nothing in your army can realistically reach the hole within a reasonable number of moves, naming it as a weakness is accurate but not yet useful — it becomes a plan only once you can point to the piece that's going there.

Provoking the weakness on purpose

Strong players don't only wait for weak squares to appear — they induce them. A well-timed pawn advance, a piece placed so that a particular pawn move becomes tempting or necessary, or simply restricting the opponent's other options until a weakening pawn move is the only reasonable one left, are all ways of manufacturing a hole rather than hoping for one. This is one of the more advanced strategic skills below master level, because it requires seeing the weakness before it exists and steering the game toward the pawn move that creates it, rather than only reacting to structures the opponent has already committed to.

Squares that look weak but aren't real weaknesses

Not every hole matters. A square with no pawn cover in the middle of nowhere, far from both kings and away from any file either side cares about, can sit unused for the whole game without costing anyone anything — a weakness only matters if a piece can occupy it and do something from there. Similarly, if the defending side can simply trade off whatever piece lands on the hole, the weakness is temporary in practice even though the pawn structure never repairs itself. Before treating a weak square as a real asset, check both that it's reachable and that the opponent can't just remove the piece that gets there.

A knight parked on a weak square with a pawn guarding it is the specific case covered on outposts; when the holes span an entire color across the whole board rather than one square, see color complex weaknesses.