Entry square

An entry square is a square from which a piece can enter enemy territory with a real purpose. Merely crossing the middle of the board is not enough: the piece should be able to attack pawns, threaten the king, occupy an important rank, or clear a route for other pieces.

The idea often appears on open files, meaning files with no pawns blocking the route. A rook may control an entire file, but the file has little value if every access square is defended. The entry square acts like a doorway: the piece must first reach it and then remain there without being driven away or exchanged immediately.

To evaluate a possible entry, check who controls the square, which piece can reach it, what target it will have afterward, and how the opponent can respond. Infiltration is the act of penetrating; the entry square is the point that makes it possible.

Defense can deny the doorway by controlling the square, blocking the route, exchanging the piece that wants to enter, or applying neutralization to a piece that has already infiltrated.