Deflection is a tactic that forces a piece of your opponent to leave the square, row or file where it has to remain, because it is needed there to defend something. This chess term is rather similar to luring, but in luring a piece has to be positioned at the right square to enable an attack while in deflection there is a (double) attack, but the defender has to be moved away in order to be successful.
Trying to promote can be seen as a kind of attack.

The following diagram is a nice example of deflection.

White threatens to promote the pawn, but then Black’s rook will capture the queened piece. Even worse: Black is also threatening to capture the pawn.
Happily for White he is able to play 53. Rg5 which prevents that the pawn can be captured (An absolute pin) and Blacks best move will be 53…Rxg5 after which Black will be able to promote 54. d8=Q.

If Black reacts to 53.Rg5 with the move 53…Kc6 then the next moves are 54.Rxd5 Kxd5 55.d8=Q+ wih an easy win for White (See mating with the queen).

In the next lesson we are going to storm the castle.