Hole

A hole is a square inside your own territory that no friendly pawn can ever control. The pawns that should have defended it have already moved past or been exchanged, and the configuration of remaining pawns means no future pawn move can ever cover the square. An enemy piece that lands there is permanent — no pawn can drive it off.

Holes are almost always created by pawn moves that looked harmless at the time. g3 creates a permanent hole on h3 and f3 if the g-pawn never returns. …e6 followed by …d5 sometimes creates a hole on d6 if Black later plays …e5. Every pawn move is also a hole move — it removes the pawn from defending the squares behind and beside it.

The square in front of a backward pawn is almost always a hole, and a hole is almost always an outpost for the opponent. The two concepts describe the same square from the two sides of the board: hole is what the defender sees, outpost is what the attacker sees.

Hole prevention is one of the basic positional disciplines. Before making any pawn move, the player should ask which squares the move uncovers and whether any future pawn move can plausibly recover them. Holes that are created accidentally are almost always permanent regrets.