Overloading (sometimes defined to children as overworking) is a chess tactic in which a defensive piece is given an additional defensive assignment which it cannot complete without abandoning its original defensive assignment.
Examples
Krasenkow vs. Karpov, in the first round of the 2003 Corus chess tournament, reached the diagrammed position with Black to play. As the white rook on f1 is tied to the defense of the pawn on f3, Black won immediately with 1... Re1!, overloading the rook: If 2.Rxe1 or 2.Qc4, then 2...Qxf3#. If 2.Kg2, then similarly, 2...Rxf1 3.Kxf1 Qxf3+ and 4...Qxd5.
In Liviu-Dieter Nisipeanu vs. Anish Giri (see diagram), Giri played 30 ...Bxh3! overloading the g2-pawn, as 31.gxh3 is met with 31...f3 (32.Re3 Qg5+).
An overload was also used in Rotlewi versus Rubinstein.