An overloaded piece (or overworked piece) is a defender with too many jobs: it protects two or more critical points at once. Since it can only fulfil one duty at a time, tactics that force it to choose win material or deliver mate.
Defense in chess is a budget, and an overloaded piece is a budget stretched past its limit. On paper, everything is defended. In reality, one defender is signed up for two contracts, and a single forcing move exposes the accounting fraud.
Black's rook on e8 performs two duties simultaneously: it defends the knight on e4, and it guards the back rank against White's rook on d1 sliding to d8. White simply captures the knight on e4. If Black recaptures with the rook, the back rank is abandoned — Rd8 arrives, back-rank mate. Black must let the knight go, a full piece for free, because the rook could not be in two places at once.
Nothing was hanging before White's capture. The knight was 'defended', the back rank was 'covered' — both statements true, both resting on the same rook. Overloading is the tactic of making both claims come due in the same move.
These three form a family, all targeting defenders rather than the defended. Overloading is the condition — one piece, multiple duties. Deflection exploits it by luring the piece away; removing the defender by capturing or trading it off. In practice the labels blur, and that's fine: what matters is the habit of auditing duties, not naming the exploit.
Run the defender audit in both directions. For your opponent: pick each defended target and identify who defends it; any defender that appears on two lists is a tactical lever, and your best moves often start there. For yourself: the moment one of your pieces becomes the sole guardian of two problems, consider the position already creaking — reinforce it before your opponent notices, not after.
A subtle version to watch: pawns count too. A pawn defending two pieces simultaneously is among the most commonly overlooked overloads at club level.
When you review your lost games, look at the move before material was lost — remarkably often, an overloaded defender was visible for several moves. Chessdock spots those recurring structures in your play and drills you on them directly.