Piezoelectric Effect
Definition
Squeeze certain crystals and they produce electricity — feed them electricity and they change shape. Your BBQ lighter uses it.
Technical definition
Mechanical stress shifts ion positions in non-centrosymmetric crystals (quartz, PZT), producing surface charge; the inverse effect converts voltage into strain.
Example
A BBQ igniter's hammer strike on a piezo crystal generates around 15,000 V — enough to spark the gas with a single click.
Common confusion
Piezoelectricity is not static electricity from rubbing. It comes from the crystal lattice deforming — no friction or contact charging is involved.