Greco’s mate is a checkmate pattern in which a rook (or queen) delivers check to the enemy king along the file it occupies, while a bishop controls the diagonal escape square, making any flight impossible. The king’s own pieces — typically unmoved pawns — block its remaining squares.
This motif most commonly arises after kingside castling, when a pawn in front of the king has advanced or disappeared, opening a file. In the most classic version, the king is driven into the corner on h8: the rook delivers mate along the h-file, and the bishop, posted on the a2-g8 diagonal (for example on b3 or c4), removes the only remaining escape square, g8. The pawn on g7 seals the last square.
In practice, this mate is especially dangerous for the side that has pushed their g- or h-pawn without a clear reason, inadvertently opening the very diagonal that leads to their downfall. Before advancing those pawns, always check whether an enemy piece can exploit the newly opened diagonal. Conversely, if you are attacking, look actively for opportunities to open that diagonal — through a pawn sacrifice or another piece sacrifice — to trigger the pattern.