The corner mate is a checkmate in which a knight delivers the final blow to a king stuck in the corner, with a rook sealing the adjacent file and the king's own pawn blocking its head.
The recipe has three ingredients: the enemy king trapped on h8, a rook (or queen) controlling the g-file so the king cannot step out of the corner, and the king's own h-pawn still on h7. A knight hopping to f7 then covers h8 and the game is over.
The knight is the perfect closer here because it attacks the corner square without standing on any line the defender could block or open. Nothing can interpose against a knight check, and from f7 the knight cannot be captured by the cornered king.
The pattern is a close cousin of the smothered mate. In the smothered version the king is buried by its own pieces on g8 and h7; in the corner mate an attacking rook does part of that work by sealing the g-file. Watch for it whenever you control the open g-file against a castled king.
In a smothered mate the king is completely surrounded by its own pieces and only the knight can reach it. In the corner mate the attacker's rook on the g-file replaces some of those blockers, but the knight still lands the final check.
Because knight checks cannot be blocked, and a knight on f7 attacks h8 while standing safely out of the king's reach. Against a king locked in the corner, one knight jump does what a queen often cannot.
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