Boden's mate
Boden's mate is a checkmate in which two bishops attack along diagonals that cross, one giving check and the other cutting off flight squares, while the king's own pieces block the rest.
Two bishops attack from different directions and cross each other's lines. One bishop gives check, the other covers the squares next to the king. The king's own pieces take the remaining squares, which is why the pattern appears when the king has castled long or stands on c8 or c1 with pieces around it.
With the black king on c8, a white bishop on a6 gives check along the diagonal through b7. A second white bishop on f4 covers c7 and b8. The black rook on d8 and knight on d7 fill the squares on the other side, so the king has no move, and neither of those pieces can capture the checking bishop.
To spot it, look for a king whose escape squares are all either covered by your bishops or occupied by its own pieces, with both bishops on open diagonals that cross. Typical squares are a6 and f4 against a king on c8, or the matching squares against a king on c1. To defend, do not leave the king on c8 with pieces crowded around it, and leave it a square to run to.
In the diagram White to move plays Ba6#. The bishop from f1 checks the king on c8 along a6, b7. The bishop on f4 covers c7 and b8, and the rook on d8 and knight on d7 block the other squares.
It sits close to Epaulette mate. An epaulette mate is a checkmate in which a queen checks a king whose two side squares are occupied by its own pieces, usually rooks, so it cannot step sideways.
Also worth reading is Swallow's tail mate. A swallow's tail mate is a checkmate in which a queen stands directly in front of the king, protected by another piece, while the king's own pieces occupy both squares beside it.
Compare it with Double check. A double check is a single move that puts the enemy king under attack from two pieces simultaneously, typically one that moved and one it unmasked, so only a king move can answer it.
Knowing "Boden's mate" helps most once you can spot it in a real game. A first lesson with George Li starts from your own games and finds the tactics you keep missing.
Related terms
Checkmate, or mate, ends a chess game at once: the king of the side to move is under attack, and none of that side's legal moves can remove the attack, so the player who delivered it wins.
An epaulette mate is a checkmate in which a queen checks a king whose two side squares are occupied by its own pieces, usually rooks, so it cannot step sideways.
The bishop pair is the advantage of owning both a light-squared and a dark-squared bishop while the opponent does not, a long-range asset that grows stronger as the position opens up.
A mating net is a setup in which the enemy king is surrounded by attackers and its own pieces so tightly that checkmate cannot be avoided, even if the final blow is a move or two away.
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