Piezoelectricity is the ability of certain crystals to produce a voltage when subjected to mechanical stress. The word is derived from the Greek piezein, which means to squeeze or press.

In a piezectric crystal, the positive and negative electrical charges are separated, but symmetrically distributed, so that the crystal overall is electrically neutral. When stress is applied, this symmetry is destroyed, and the charge asymmetry generates a voltage.

Richard Wegner