Smothered mate
A smothered mate is checkmate by a knight when the king’s own pieces take away all of its flight squares.
The knight does not need help from another attacking piece. The king’s own rook and pawns do the trapping. That is why the mate is so short: there is no square to run to and nothing can capture the knight.
Nf7# lands next to a king on h8 that is sealed in by the rook on g8 and the pawns on g7 and h7. The knight is safe from the king, and no other black piece attacks f7.
The usual route to this mate is a queen check that attracts a rook to g8, then the knight hop. The attraction page shows that first half; this page is the finish.