Deflection vs decoy: leaving a square, or arriving at one
Both are usually sacrifices, both look like blunders on the move they are played, and they are told apart by which square you care about.
The difference in one sentence
Deflection forces an enemy piece to leave the square or line it was defending -- you care about the square it is leaving. Decoy, also called attraction, forces an enemy piece onto a specific square -- you care about the square it arrives on.
The confusion is understandable, because the same move can sometimes be both, and because both are typically executed by giving material away. The way to keep them apart is to finish the sentence 'this move wins because...'. If the answer names a square that is now unguarded, it was a deflection. If it names a square that now has an enemy piece standing on it, it was a decoy.
The most common decoy in chess drags the enemy king out. A check that the king must accept, onto a square where a knight fork or a discovered attack is waiting, is the classic version, and it is why so many king hunts begin with a queen sacrifice.
The most common deflection is against an overloaded piece -- one that is defending two things at once. Attack the less important of the two, and the more important one falls.
One of each
Deflection
Position 1
Black to move. Find the best move.
Show the answer
39.Re1 39...Bd3+ 40.Kg2 40...Rxe1
The line wins a rook. The defender is dragged off the square it was guarding, and the square decides the position the moment it is unguarded.
The position comes from an endgame of a real game, rated 830 for difficulty. The answer reaches a winning advantage.
Attraction
Position 2
Black to move. Find the best move.
Show the answer
27.Rxa6 27...Rxb1+ 28.Kxb1 28...Rc1#
The line ends in checkmate. The sacrifice exists to put an enemy piece on one specific square, because on that square a follow-up tactic works.
The position comes from the middlegame of a real game, rated 650 for difficulty. The answer reaches checkmate.
Questions people ask
What is the difference between deflection and decoy?
Deflection forces a piece away from a square or line it is defending. A decoy, also called attraction, forces a piece onto a square where it becomes vulnerable. One is about the square being abandoned; the other about the square being occupied.
Is attraction the same as a decoy?
Yes. Lichess and most modern tactics trainers use 'attraction'; older chess literature usually says 'decoy' or 'lure'. They describe the same tactic.
Can one move be both a deflection and a decoy?
It can, and quite often is. A sacrifice that pulls a defending rook off the back rank and onto a square where it is forked is doing both jobs at once. The names are descriptions of purpose, not exclusive categories.