Smothered Mate
A smothered mate is a checkmate — almost always by a knight — where the enemy king is boxed in by its own pieces and has no square to escape to. The king is literally smothered by its own army.
The knight on f7 has delivered checkmate. The black king is smothered by its own rook on g8 and the g7/h7 pawns, so the knight check is mate.
Source for further study: Polgar, Chess in 5334 Positions.