Piezo transducer we also called piezo passive buzzer. Piezoelectric transducers will not produce sound when connected to direct current, and need to connect an external audio output circuit to produce sound. Because of this, its sounds are diverse, and the types of sounds are richer, and simple songs can be played.
Piezo transducer is driven by square wave (VP-P), the advantage is the sound frequency controllable, power consumption is small, generally in 20ma below, not more than 100ma. So, when you see a buzzer specification, if the voltage shows Vp-p, you can be sure that this is a passive buzzer.