These are all tactics that involve taking advantage of a defending unit. The defending piece can be destroyed, deflected, decoyed or overloaded.

Destruction

A key piece is holding a position together; capture it and the position falls apart.

If it can be removed by an immediate capure, this is often worth doing even if it involves a heavy loss of material

Deflection

Also known as distraction: when a piece has been deflected away from a vital square or line

Decoy

Also known as enticement: different from deflection because the piece has been tempted onto a fatal square or line

Overloading

a piece is over-loaded when it is performing two or more vital roles (for example, defedning two pieces, or against a mate threat and a pawn promotion). If it can be forced to perform one role then it cannot perform the other