Buzzer vs piezo sound for generating sound
By piezo you most likely mean a piezo speaker, is a electromechanical device that converts electric energy (AC voltage) into sound energy (sound wave) and vice versa. Buzzer name is used as a device that needs a DC power supply that has in built a tone generator, power driver and piezo speaker. This tone generator and power driver can be one transitor, capacitor and some resistor.

What&#39;s the third wire on a piezo buzzer?