The Triangle Mate, also known as the Fish Tail Mate, is a queen and rook checkmate pattern that resembles the visual appearance of a triangle (or a fish tail for that matter).
Triangle Mate Example
Diagram above: 1.Qf5# is a simple demonstration of the Triangle Mate. Note how the white queen, white rook and black pawn on g7 resemble a triangle around the black king.
Interesting Notes on the Triangle Mate
The Triangle Mate (in combination with the Kill Box Mate) is an important “ingredient” in a checkmate method known as the RailRoad Mate.