A buzzer or beeper is an audio signaling device, which may be mechanical, electromechanical, or piezoelectric. Piezoelectric buzzers, or piezo buzzers, are devided into 3 main types: passvie piezo buzzers, active piezo buzzers and self drive piezo buzzers.
Passive piezo buzzers, also known as piezo transducers, consist of a casing, a piezo element and a terminal, and you need external driving signal to operate the buzzer, therefore, with greater range of flexibility of frequencies when designing PCB circuit.