Decoy is a piece sacrifice in chess made in order to get an advantage by forcing the opponent piece to change its position.
Let's see an example.
Diagram 1
1. Qh7 Queen sacrifice by White. Black King is obligated to capture the Queen.
If not 1. ... Kf8 2. Qh8 checkmate.
Diagram 2
After King captures the Queen , Discovered check by Bishop . Rook controls the escape squares of the opponent King.
1. ... Kxh7 2. Re8 mate.